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ABSTRACT
Spark ignition engines utilize ignition systems that can developup to about 30 kV for breakdown of the spark plug gap and
typically deliver current levels in the range of 30 to 100 mA.
easurement and analysis of these systems show that the
energy transfer e!ciency is very low" typically in the order of
one percent #1$% or less. &his operating level is ade'uate for
older and most modern engines" but will not meet the needs of
future lean burn and some alternate fuel engines that re'uire
higher energy discharges to e(ectively ignite the air)fuelmi*tures. &o meet the re'uirements for increased ignition
power and energy" ignition systems will have to be designed to
operate at higher transfer e!ciencies. &here are two basic
approaches to increasing the electrical e!ciency of ignition
systems. &he +rst is to utilize peaking capacitors across the
spark plug. &he second is to design and utilize a more e!cient
discharge circuit in combination with a low resistance spark
coil. A third alternative would be to utilize a combination ofboth. ,y the +rst method" transfer e!ciency can be increased
to nearly +fty percent #-0$%. ,y the third" transfer e!ciency
can be seventy+ve percent #/-$% or more. &his paper
summarizes the results of high power ignition e*periments and
related analyses" for socalled breakdown ignition conditions.
&he paper includes descriptions of both conventional system
upgrades and a new higher energy system that features
multiple drivers and an energy recovery circuit. t does notinclude analyses or e*periments for arc or glow discharge
conditions.
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Introduction
Learning Objective:
dentify charging" starting" ignition" and accessorycircuit
components" their functions" and maintenance procedures.
dentify the basic types of automotive wiring" types of
terminals" and wiring diagrams. &he electrical systems on
e'uipment used by the 2avy are designed to perform a variety
of functions. &he automotive electrical system contains +ve
electrical circuits.
&hese circuits are as follows #+g. 1%4
1. 5harging circuit". Starting circuit"3. gnition circuit6. 7ighting circuit-. Accessory circuit
8lectrical power and control signals must be delivered to
electrical devices reliably and safely so electrical system
functions are not impaired or converted to hazards. &his goal is
accomplished through careful circuit design" prudent
component selection" and practical e'uipment location. ,y
carefully studying this chapter and the preceding chapter" you
will understand how these circuits work and the ad9ustments
and repairs re'uired to maintain the electrical systems in peak
condition.
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Learning Objective: dentify chargingcircuit components"
their functions" and maintenance procedures. &he charging
system performs several functions" which are as follows4 t
recharges the battery after engine cranking or after the use of
electrical accessories with the engine turned o(. t supplies all
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the electricity for the vehicle when the engine is running. t
must change output to meet di(erent electrical loads.
t provides a voltage output that is slightly higher than battery
voltage. A typical charging circuit consists of the following4
,A&&8:; provides current to energize or e*cite the alternator
and assists in stabilizing initial alternator output. A7&8:2A&
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BATTERY CONSTRUCTION&he leadacid celltype storage battery is built to withstand
severe vibration" cold weather" engine heat" corrosive
chemicals" high current discharge" and prolonged periods
without use. &o test and service batteries properly" you must
understand battery construction. &he construction of a basic
leadacid celltype battery is as follows4
,attery element
,attery case" cover" and caps
8lectrolyte
,attery terminals
BATTERY ELEMENT.
&he battery element is made up of negative plates" positive
plates" separators" and straps #+g. 3%. &he element +ts into a
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cell compartment in the battery case. ost automotive
batteries have si* elements.
8ach cell compartment contains two kinds of chemically activelead plates" known as positive and negative plates. &he battery
plates are made of =:? #sti( mesh framework% coated with
porous lead. &hese plates are insulated from each other by
suitable separators and are submerged in a sulfuric acid
solution #electrolyte%.
5harged negative plates contain spongy #porous% lead #@b%which is gray in color. 5harged positive plates contain lead
pero*ide #@b
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#microporous rubber" +brous glass" or plasticimpregnated
material%" called separators" are inserted between the plates.
&hese separators are thin and porous so the electrolyte will ow
easily between the plates. &he side of the separator that is
placed against the positive plate is grooved so the gas that
forms during charging will rise to the surface more readily.
&hese grooves also provide room for any material that akes
from the plates to drop to the sediment space below.
BATTERY CASE COYER AN! CA"S#
&he battery case is made of hard rubber or a high 'uality
plastic. &he case must
withstand e*treme vibration" temperature change" and the
corrosive action of the
electrolyte. &he dividers in the case form individual containers
for each element. A container with its element is one cell.
Sti( ridges or ribs are moulded in the bottom of the case to
form a support for the plates and a sediment recess for the
akes of active material that drop o( the plates during the life
of the battery. &he sediment is thus kept clear of the plates so it
will not cause a short circuit across them.
&he battery cover is made of the same material as the
container and is bonded to and seals the container. &he cover
provides openings for the two battery posts and a cap for each
cell.
,attery caps either screw or snap into the openings in the
battery cover. &he battery caps #vent plugs% allow gas to
escape and prevent the electrolyte from splashing outside the
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battery. &hey also serve as spark arresters #keep sparks or
ames from igniting the gases inside the battery%. &he battery
is +lled through the vent plug openings. aintenancefree
batteries have a large cover that is not removed during normal
service.
CAUTION
Bydrogen gas can collect at the top of a battery. f this gas is
e*posed to a ame or spark" it can e*plode.
BATTERY TERMINALS#$ ,attery terminals provide a means of
connecting the battery plates to the electrical system of the
vehicle. 8ither two round post or two side terminals can be
used.
,attery terminals are round metal posts e*tending through the
top of the battery cover. &hey serve as connections for battery
cable ends. @ositive post will be larger than the negative post. t
may be marked with red paint and a positive #C% symbol.
2egative post is smaller" may be marked with black or green
paint" and has a negative #% symbol on or near it.
Side terminals are electrical connections located on the side of
the battery. &hey have internal threads that accept a special
bolt on the battery cable end. Side terminal polarity is identi+ed
by positive and negative symbols marked on the case.
ELECTROLYTE# &he electrolyte solution in a fully charged
battery is a solution of concentrated sulphuric acid in water.
&his solution is about D0 percent water and about 60 percent
sulphuric acid. &he electrolyte in the leadacid storage battery
has a speci+c gravity of 1.E" which means that it is 1.E times
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as heavy as water. &he amount of sulphuric acid in the
electrolyte changes with the amount of electrical chargeF also
the speci+c gravity of the electrolyte changes with the amount
of electrical charge. A fully charged battery will have a speci+c
gravity of 1.E at E0G H. &he +gure will go higher with a
temperature decrease and lower with a temperature increase.
electrolyte changes with the amount of electrical chargeF also
the speci+c gravity of the electrolyte changes with the amount
of electrical charge. A fully charged battery will have a speci+c
gravity of 1.E at E0G H. &he +gure will go higher with a
temperature decrease and lower with a temperature increase.
As a storage battery discharges" the sulphuric acid is depleted
and the electrolyte is gradually converted into water. &his
action provides a guide in determining the state of discharge of
the leadacid cell. &he electrolyte that is placed in a leadacid
battery has a speci+c gravity of 1.E0.
&he speci+c gravity of an electrolyte is actually the measure of
its density. &he
electrolyte becomes less dense as its temperature rises" and a
low temperature means a high speci+c gravity. &he hydrometer
that you use is marked to read speci+c gravity at E0G H only.
>nder normal conditions" the temperature of your electrolyte
will not vary much from this mark. Bowever" large changes in
temperature re'uire a correction in your reading.
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Hor 8V8:; 10degree change in temperature A,,&:A5& 0.006 from your speci+c gravity reading. Suppose
you have 9ust taken the gravity reading of a cell. &he
hydrometer reads 1.E0. A thermometer in the cell indicates an
electrolyte temperature of D0G H. &hat is a normal di(erence of
0 degrees from the normal of E0G H. &o get the true gravity
reading" you must subtract 0.00E from 1.E0. &hus the speci+c
gravity of the cell is actually 1./. A hydrometer conversion
chart similar to the one shown in +gure 6 is usually found on
the hydrometer. Hrom it" you can obtain the speci+c gravity
correction for temperature changes above or below E0G H.
Higure 6. Bydrometer conversion chart.
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BATTERY CA"ACITY
&he capacity of a battery is measured in amperehours. &he
amperehour capacity is e'ual to the product of the current in
amperes and the time in hours during which the battery is
supplying current. &he amperehour capacity varies inversely
with the discharge current. &he size of a cell is determined
generally by its amperehour capacity. &he capacity of a cell
depends upon many factors" the most important of which are
as follows4
1. &he area of the plates in contact with the electrolyte
. &he 'uantity and speci+c gravity of the electrolyte
3. &he type of separators
6. &he general condition of the battery #degree of sulfating"
plates buckled" separators warped" sediment in bottom of cells"
etc.%
-. &he +nal limiting voltage
Batter% Rating&
,attery ratings were developed by the Society of Automotive
8ngineers #SA8% and the ,attery 5ouncil nternational #,5%.
&hey are set according to national test standards for battery
performance. &hey let the mechanic compare the cranking
power of one battery to another. &he two methods of rating
leadacid storage batteries are the cold cranking rating and the
reserve capacity rating.
COL!$CRAN'ING RATING#$ &he coldcranking rating
determines how much current in amperes the battery can
deliver for thirty seconds at 0G H while maintaining terminal
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&here are several methods for charging batteriesF only direct
current is used with each method. f only alternating current is
available" a recti+er or motor generator must be used to
convert to direct current. &he two principal methods of charging
are #1% constant current and #% constant voltage #constant
potential%. 5onstant current charging is be used on a single
battery or a number of batteries in series. 5onstant voltage
charging is used with batteries connected in parallel. #A parallel
circuit has more than one path between the two source
terminalsF a series circuit is a onepath circuit%. ;ou should know
both methods" although the latter is most often used.
CONSTANT CURRENT C)ARGING#$
Iith the constant current method" the battery is connected to a
charging device that supplies a steady ow of current. &he
charging device has a recti+er #a gas+lled bulb or a series of
chemical disks%F thus" the alternating current is changed into
direct current. A rheostat #resistor for regulating current% of
some kind is usually built into the charger so that you can
ad9ust the amount of current ow to the battery.
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remains constant for hours" you can assume that the battery
will take no more charge.
&he primary disadvantage of constant current charging is that
&B8 5BA:=2= 5>::82& :8A2S A& A S&8A?; VA7>8 >278SS
; 5BA2=8 &. A battery charged with too high current rate
would overheat and damage the plates" making the battery
useless. ?o 2
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t is easy to connect the battery to the charger" turn the charging
current on" and" after a normal charging period" turn the charging
current o( and remove the battery. 5ertain precautions however are
necessary both ,8H:2= the charging period. &hese
practices are as follows4 1. 5lean and inspect the battery thoroughly
before placing it on charge. >se a solution of baking soda and water
for cleaningF and inspect for cracks or breaks in the container.
"LACING NE* BATTERIES IN SER(ICE
2ew batteries may come to you full of electrolyte and fully
charged. n this case" that is necessary is to install the batteries
properly in the piece of e'uipment. ost batteries shipped to
25H units are received charged and dry.
5harged and dry batteries will retain their state of full charge
inde+nitely so long as moisture is not allowed to enter the cells.
&herefore" batteries should be stored in a dry place. oisture
and air entering the cells will allow the negative plates to
o*idize. &he o*idation causes the battery to lose its charge. &o
activate a dry battery" remove the restrictors from the vents
and remove the vent caps. &hen +ll all the cells to the proper
level with electrolyte. &he best results are obtained when the
temperature of the battery and electrolyte is within the range
of D0G H to E0G H.
Some gassing will occur while you are +lling the battery due to
the release of carbon dio*ide that is a product of the drying
process of the hydrogen sul+de produced by the presence of
free sulphur. &herefore" the +lling operations should be in a
wellventilated area. &hese gases and odours are normal and
are no cause for alarm.
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Appro*imately - minutes after adding electrolyte" the battery
should be checked for voltage and electrolyte strength. ore
than D volts or more than 1 volts" depending upon the rated
voltage of the battery" indicates the battery is ready for service.
Hrom - to D volts or from 10 to 1 volts indicate o*idized
negative plates" and the battery should be charged before use.
7ess than - or less than 10 volts" depending upon the rated
voltage" indicates a bad battery" which should not be placed in
service.
f" before placing the battery in service" the speci+c gravity"
when corrected to E0G H" is more than .030 points lower than it
was at the time of initial +lling or if one or more cells gas
violently after adding the electrolyte" the battery should be fully
charged before use. f the electrolyte reading fails to rise during
charging" discard the battery. f" before placing the battery in
service" the speci+c gravity" when corrected to E0G H" is more
than .030 points lower than it was at the time of initial +lling or
if one or more cells gas violently after adding the electrolyte"
the battery should be fully charged before use. f the electrolyte
reading fails to rise during charging" discard the battery.
ost shops receive readymi*ed electrolyte. Some units may
still get concentrated sulphuric acid that must be mi*ed with
distilled water to get the proper speci+c gravity for electrolyte.
L2= 8785&:
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may re'uire hours of safe dilution.
Higure - shows you how much water and acid to mi* for
obtaining a certain speci+c gravity. Hor e*ample" mi*ing - parts
of water to parts of acid produces an electrolyte of 1.300"
when starting with 1.E3- speci+c gravity acid. f you use 1.600
speci+c gravity acid" parts water and - parts acid will give the
same results.
7et the mi*ed electrolyte cool down to room temperature
before adding it to the
battery cells. Bot electrolyte will eat up the cell plates rapidly.
&o be on the safe side" do not add the electrolyte if its
temperature is above K0G H. After +lling the battery cells" let the
electrolyte cool again because more heat is generated by its
contact with the battery plates. 2e*t" take hydrometer
readings. &he speci+c gravity of the electrolyte will correspond
'uite closely to the values on the mi*ing chart if the parts of
water and acid are mi*ed correctly.
BATTERY MAINTENANCE
f a battery is not properly maintained" its service life will be
drastically reduced. ,attery maintenance should be done
during every @ cycle. 5omplete battery maintenance includes
the following4
Visually checking the battery.
5hecking the electrolyte level in cells on batteries with caps.
Adding water if the electrolyte level is low.
5leaning o( corrosion around the battery and battery terminals.
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Higure -. 8lectrolyte mi*ing chart.
BATTERY TEST
As a mechanic you will be e*pected to test batteries for proper
operation and
condition. &hese tests are as follows4
,attery leakage test
,attery terminal test,attery voltage test
5ell voltage test
,attery drain test
,attery load test #battery capacity test%
Muick charge test
BATTERY LEA'AGE TEST#$ A battery leakage test will
determine if current is discharging across the top of the battery.
A dirty battery can discharge when not in use. &his condition
shortens battery life and causes starting problems.
&o perform a battery leakage test" set a voltmeter on a low
setting. &ouch the probes on the battery" as shown in +gure D.
f any current is registered on the voltmeter" the top of the
battery needs to be cleaned.
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BATTERY TERMINAL TEST#$&he battery terminal test 'uickly
checks for poor electrical connection between the terminals
and the battery cables. A voltmeter is used to measure voltage
drop across terminals and cables.
&o perform a battery terminal test #+g. /%" connect the
negative voltmeter lead to the battery cable end. &ouch the
positive lead to the battery terminal. Iith the ignition or
in9ection system disabled so that the engine will not start" crank
the engine while watching the voltmeter reading.
Higure D. ,attery leakage test. Higure /. ,attery
terminal test.
BATTERY (OLTAGE TEST#
&he battery voltage test is done by measuring total battery voltage
with an accurate voltmeter or a special battery tester #+g. E%. &his
test determines the general state of charge and battery condition
'uickly.
&he battery voltage test is used on maintenancefree batteries
because these batteries do not have caps that can be removed for
testing with a hydrometer. &o perform this test" connect thevoltmeter or battery tester across the battery terminals. &urn on the
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vehicle headlights or heater blower to provide a light load. 2ow read
the meter or tester. A wellcharged battery should have over 1
volts. f the meter reads appro*imately 11.- volts" the battery is not
charged ade'uately" or it may be defective.
CELL (OLTAGE TEST#
&he cell voltage test will let you know if the battery is discharged or
defective. 7ike a
hydrometer cell test" if the voltage reading on one or more cells is .
volts or more lower than the other cells" the battery must be
replaced. &o perform a cell voltage test #+g. K%" use a low voltage
reading voltmeter with special cadmium #acid resistant metal% tips.
nsert the tips into each cell" starting at one end of the battery and
work your way to the other. &est each cell carefully. f the cells are
low" but 'uall recharging usually will restore the battery. f cell
voltage readings vary more than . volts" the battery is ,A?.
Higure E. ,attery voltage test performed with a battery tester.
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Higure K. 5ell voltage test.
,A&&8:; ?:A2 &8S&. A battery drain test checks for abnormal
current draw
with the ignition o(. f a battery goes dead without being used" you
need to check for a current drain.
&o perform a battery drain test" set up an ammeter" as shown in
+gure 10. @ull the fuse if the vehicle has a dash clock. 5lose
all doors and trunk #if applicable%. &hen read the ammeter. f
everything is o(" there should be a zero reading. Any reading
indicates a problem. &o help pinpoint the problem" pull fuses
one at a time until there is a zero reading on the ammeter. &his
action isolates the circuit that has the problem.
BATTERY CA"ACITY TEST#$
A battery load test" also termed a battery capacity test" is the
best method to check battery condition. &he battery load test
measures the current output and performance of the battery
under full current load. t is one of the most common and
informative battery tests used today.
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,efore load testing a battery" you must calculate how much
current draw should be applied to the battery. f the ampere
hour rating of the battery is given" load the battery to three
times its amphour rating. Hor e*ample" if the battery is rated at
D0 amphours" test the battery at 1E0 amps #D0 * 3 N 1E0%. &he
ma9ority of the batteries are now rated in SA8 coldcranking
amps" instead of amphours. &o determine the load test for
these batteries" divide the coldcrank rating by two. Hor
e*ample" a battery with 600 cold cranking amps rating should
be loaded to 00 amps #600 O N 00%. 5onnect the battery
load tester" as shown in +gure 11. &urn the control knob until
the ammeter reads the correct load for your battery.
After checking the battery charge and +nding the amp load
value" you are ready to test battery output. ake sure that the
tester is connected properly. &urn the load control knob until the
ammeter reads the correct load for your battery. Bold the load
for 1- seconds. 2e*t" read the voltmeter while the load is
applied.
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+UIC' C)ARGE TEST#$
&he 'uick charge test" also known as 3minute charge test"
determines if the battery is sulphated. f the results of the
battery load test are poor" fast charge the battery. 5harge the
battery for 3 minutes at 30 to 60 amps. &est the voltage while
charging. f the voltage goes A,
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must be constructed according to the number of +eld poles because
current is generated when the coil #winding on the armature% moves
across each magnetic circuit. Higure 1. Sectional view of a dc
generator. &he current is collected from the armature coils by
brushes #usually made of carbon% that make rubbing contact with a
commentator. &he commutator consists of a series of insulated
copper segments mounted on one end of the armature" each
segment connecting to one or more armature coils. &he armature
coils are connected to the e*ternal circuits #battery" lights" or
ignition% through the commutator and brushes. 5urrent induced in
the armature coils thus is able to ow to the e*ternal circuits. &here
are two types of +eld circuits" determined by the point at which the
+eld circuit is grounded" which are as follows4
Higure 1. Sectional view of a dc generator
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IGNITION CIRCUIT
&he ignition circuit supplies high voltage surges #some as high
as -0"000 volts in electronic ignition circuits% to the spark plugs
in the engine cylinders. &hese surges produce electric sparks
across the spark plug gaps. &he heat from the spark ignites the
compressed airfuel mi*ture in the combustion chambers. Ihen
the engine is idling" the spark appears at the spark plug gap
9ust as the piston nears top dead center #&?5% on the
compression stroke. Ihen the engine is operating at higher
speeds" the spark is advanced. t is moved ahead and occurs
earlier in the compression stroke. &his design gives the
compressed mi*ture more time to bum and deliver its energy to
the pistons. &he functions of
an ignition circuit are as follows4
1. @rovide a method of turning the ignition circuit
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D. Vary spark timing with engine speed" load" and other
conditions.
"RIMARY AN! SECON!ARY CIRCUITS
&he ignition circuit is actually made of two separate circuits
which work together to cause the electric spark at the spark
plugs. &hese two circuits are the @:A:; and S85
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!"#!T!$# 0!%TR!B1T$R- distri+utesignition voltage to the spar2 plug.
'ontains either mechanical contact points or an electronic switching circuit.
%3AR4 3*1"- device that provides an air gap in the com+ustion cham+er for
an electric arc.
Ignition S.itc/
&he ignition switch #+g. 63% enables the operator to turn the
ignition on for starting and running the engine and to turn it o(
to stop the engine. ost automotive ignition switches
incorporate four positions" which are as follows4
O00
&he
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terminals #low voltage connections%" an iron core #long piece of
iron inside the windings%" and a high voltage terminal #coil wire
connection%. &he primary winding is the outer winding and is
made up of several hundred turns of heavy wire" wrapped
around or near the secondary winding. &he secondary winding
is the inner winding and is made up of several thousand turns
of heavy wire located inside or near the primary winding. &he
secondary windings are wound in the opposite direction of the
primary" and the ends are attached internally to the primary
windings and the high voltage terminal. ,oth windings are
wrapped around an iron core and are housed inside the coil
case. &o obtain the high current re'uired for ignition" battery
current ows through the ignition coil primary windings
producing a strong magnetic +eld. &he action of the iron core
strengthens the magnetic +eld.
)igure 6-77.- %ectional view of an ignition coil
&hen the current flowing through the coil is +ro2en (the primar, circuit is
opened/ the magnetic field collapses across the secondar, windings. As the
magnetic field collapses/ a high
electrical voltage is induced into the
secondar, circuit. %ince +oth the
primar, and secondar, windings of the
coil are stationar,/ some means otherthan movement of the windings must
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+e found to change the magnetic field surrounding the coils. !n practice/ a
switching device in the primar, circuit creates this effect. There are two
common methods to +rea2 current flow and fire the coil mechanical contact
points or an electronic switching device.
IGNITION !ISTRIBUTOR
An ignition distributor can be a contact point or pickup coil
type" as shown in +gure 6-. A contact point distributor is
commonly found in older vehicles" whereas the pickup coil type
distributor is used on many modern vehicles. &he ignition
distributor has several functions" which are as follows4
t actuates the
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Higure 6-. 5omparison of a #A% contact point distributor and a
#,% pickup coil
?istributor.
!ISTRIBUTOR CA"#$&he distributor cap is an insulating plastic
component that
covers the top of the distributor housing. ts centre terminal
transfers voltage from the coil wire to the rotor. &he distributor
cap also has outer terminals that send electric arcs to the spark
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plugs. etal terminals are molded into the plastic cap to
provide electrical connections.
!ISTRIBUTOR ROTOR#$&he distributor rotor transfers voltage
from the coil wire to the spark plug wires. &he rotor is mounted
on top of the distributor shaft. t is an electrical switch that
feeds voltage to each spark plug wire in turn.
A metal terminal on the rotor touches the distributor cap center
terminal. &he outer end of the rotor A7
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vehicles re'uire resistor type plugs. 2onresistor spark plug has
a solid metal rod forming the center electrode. &his type of
spark plugs is 2
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the plug. &hen high voltage surges would leak across the
carbon instead of producing a spark across the spark plug gap.
>sing a hotter plug will bum this carbon deposit away or
prevent it from forming. Spark plug reach is the distance
between the end of the spark plug threads and the seat or
sealing surface of the plug. @lug reach determines how far the
plug reaches through the cylinder head. f spark plug reach is
too long" the spark plug will protrude too far into the
combustion chamber and the piston at &?5 may strike the
electrode.
Bowever" if the reach is too short" the plug electrode may not
e*tend far enough into the cylinder head and combustion
e!ciency will be reduced. A spark plug must reach into the
combustion chamber far enough so that the spark gap will be
properly positioned in the combustion chamber without
interfering with the turbulence of the airfuel mi*ture or
reducing combustion action.
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)igure 6-78.- %ectional view of a (A non-resistor and (B resistor spar2 plug.
S"AR' "LUG *IRES
&he spark plug wires carry the high voltage electric current
from the distributor cap side terminals to the spark plugs. n
vehicles with distributorless ignition" the spark plug wires carry
coil voltage directly to the spark plugs. &he two types of spark
plug wires are as follows4
S
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ohms per foot. &his prevents highvoltage induced
popping or cracking of the radio speakers.
&
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5
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ELECTRONIC IGNITION SYSTEM&he basic di(erence between the contact point and the
electronic ignition system is in the primary circuit. &he primary
circuit in a contact point ignition system is open and closed by
contact points. n the electronic system" the primary circuit is
open and closed by the electronic control unit #85>%.
&he secondary circuits are practically the same for the twosystems. &he di(erence is that the distributor" ignition coil" and
wiring are altered to handle the high voltage produced by the
electronic ignition system.
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@5Q>@ 5 dwell time #number of degrees the circuit conducts
current to the ignition coil% is designed into the electronic circuit
of the 85> and is 2
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current passes through the primary windings of the ignition coil"
thereby developing a magnetic +eld. &hen" when the trigger
wheel and pickup coil turn " the magnetic +eld
inside the ignition coil collapses and +res a sparkplug.
)a33$E5ect Sen&or
Some electronic distributors have a magnetic sensor using the
Ball e(ect. Ihen a steel shutter moves between the two poles
of a magnet" it cuts o( the magnetism between the two poles.
&he Balle(ect distributor has a rotor with curved plates" called
shutters. &hese shutters are curved so they can pass through
the air gap between the two poles of the magnetic sensor" as
the rotor turns. 7ike the trigger wheel" there are the same
number of shutters as there are engine cylinders.
8ach time a shutter mo ves through the air gap between the
two poles of the magnetic sensor" it cuts o( the magnetic +eld
between the poles. &his action provides a signal to the 85>.
Ihen a shutter is not in the way" the magnetic sensor is
producing voltage. &his voltage is signaling the 85> to allow
current to ow through the ignition coils primary winding.
Bowever" when the shutter moves to cut o( the magnetic +eld"
the signal voltage drops to zero. &he 85> then cuts o( the
current to the ignition coils primary winding. &he magnetic +eld
collapses" causing the coil secondary winding to produce a high
voltage surge. &his high voltage surge is sent by the rotor to
the proper spark plug.
IGNITION TIMING !E(ICES
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gnition timing refers to how early or late the spark plugs +re in
relation to the position of the engine pistons. gnition timing
must vary with engine speed" load" and temperature.
&iming advance happens when the spark plugs +re sooner than
the compression strokes of the engine. &he timing is set several
degrees before top dead center #&?5%.
ore time advance is re'uired at higher speeds to give
combustion enough time to develop pressure on the power
stroke.&iming retard happens when the spark plugs +re later on
the compression strokes. &his is the opposite of timing
advance. Spark retard is re'uired at lower speeds and under
high load conditions. &iming retard prevents the fuel from
burning too much on the compression stroke" which would
cause spark knock or ping.
&he basic methods to control ignition system timing are as
follows4
582&:H>=A7 A?VA258 #controlled by engine speed%
VA5>> A?VA258 #controlled by intake manifold vacuum and
engine load%
5&8:R8? A?VA258 #controlled by various sensors
speed" temperature"
intake" vacuum" throttle position" etc.%
Centri6uga3 Advance
5entrifugal advance makes the ignition coil and spark plugs +re
sooner as engine speed increases" using springloaded weights"
centrifugal force" and lever action to rotate the distributor cam
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or trigger wheel. Spark timing is advanced by rotating the
distributor cam or trigger wheel against distributor shaft
rotation. &his action helps correct ignition timing for ma*imum
engine power. ,asically the centrifugal advance consists of two
advance weights" two springs" and a advance lever.
?uring periods of low engine speed" the springs hold the
advance weights inward towards the distributor cam or trigger
wheel. At this time there is not enough centrifugal force to push
the weights outward. &iming stays at its normal initial setting.
As speed increases" centrifugal force on the weights moves
them outwards against spring tension. &his movement causes
the distributor cam or trigger wheel to move ahead. Iith this
design" the higher the engine speed" the faster the distributor
shaft turns" the farther out the advance weights move" and the
farther ahead the cam or trigger wheel is moved forward or
advanced. At a preset engine speed" the lever strikes a stop
and centrifugal advance reaches ma*imum.
&he action of the centrifugal advance causes the contact points
to open sooner" or the trigger wheel and pickup coil turn o( the
85> sooner. &his causes the ignition coil to +re with the engine
pistons not as far up in the cylinders.
(acuu4 Advance
&he vacuum advance provides additional spark advance when
engine load is low at part throttle position. t is a method of
matching ignition timing with engine load. &he vacuum
advance increases H>87 85
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of a vacuum diaphragm" link" movable distributor plate" and a
vacuum supply hose.
At idle" the vacuum port from the carburetor or throttle body to
the distributor advance is covered" thereby 2< vacuum is
applied to the vacuum diaphragm" and spark timing is 2
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82=28 5
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open throttle and other sensor outputs say the same. &he
computer receives and calculates the data" then" if re'uired"
retards ignition timing to prevent spark knock or ping.
IGNITION SYSTEM MAINTENANCE
gnition troubles can result from a myriad of problems" from
faulty components to loose or damaged wiring. >nless the
vehicle stops on the 9ob" the operator will report trouble
indications" and the e'uipment is turned into the shop for
repairs.
>nless the trouble is known" a systematic procedure should be
followed to locate the cause. :emember" that electric current
will follow the path of least resistance. &race ignition wiring
while checking for grounds" shorts" and open circuits. ,are
wires" loose connections" and corrosion are found through
visual inspection.
After checking the system" you must evaluate the symptoms
and narrow down the possible causes. >se your knowledge of
system operation" a service manual troubleshooting chart"
basic testing methods" and common sense to locate the
trouble. any shops have specialized e'uipment that provide
the mechanic a 'uick and easy means of diagnosing ignition
system malfunctions.
S1ar2 "3ug& and S1ar2 "3ug *ire&
,ad spark plugs cause a wide range of problems mis+ring" lack
of power" poor fuel economy" and hard starting. After prolonged
use" the spark pl ug tip can become coated with ash" oil" and
other residue. &he spark plug electrodes can also bum and
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widen the gap. &his makes it more di!cult for the ignition
system to produce an electric arc between the electrodes.
&o read spark plugs closely" inspect and analyze the condition
of each spark plug tip and insulator. &his will give you
information on the condition of the engine" the fuel system" and
the ignition system. &he conditions commonly encountered with
spark plugs areas follows4
2
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)igure 6-79.-
#ormal operation.
)igure 6-7.- 'ar+on fouled.
)igure 6-7;.- $il fouled.
ASB H78? #+g. -0% appears as
red" brown" yellow" or white
coloured deposits which
accumulate on the insulator"
resulting from poor fuel 'uality or
oil entering the cylinder. ost ash
deposits have no adverse e(ect on
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the operation of the spark plug as long as they remain in a
powdery state. Bowever" under certain conditions these
deposits melt and form a shiny glaze on the insulator which"
when hot" acts as a good electrical conductor. &his allows
current to follow the deposit instead of 9umping the gap" thus
shorting out the spark plug. Spark plugs" having a powdery
condition" may be cleaned" regapped" and replaced. &hose
having a glazed deposit are to be replaced.
@:8=2&
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)igure 6-
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reaching the spark plugs. &o test the wires for proper operation"
you can perform the following4
A SPARK PLUG WIRE RESISTANCE TEST
Iill check the spark plug conductor or coil wire conductor. &o
perform a wire resistance test" connect an ohmmeter across
each end of the wire. &he meter will read internal wire
resistance in ohms. &ypically resistance should 2
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timing" and distributes high voltage to the spark plugs. f any
part of the distributor is faulty" engine performance su(ers.
!ISTRIBUTOR CA" AN! ROTOR#$ Ihen problems point to
possible distributor
cap or rotor troubles" remove and inspect them. &he distributor
cap should be carefully checked to see that sparks have not
been arcing from point to point. ,oth interior and e*terior must
be clean. &he +ring points should not be eroded" and the
interior of the towers must be clean.
&he rotor tip" from which the hightension spark 9umps to each
distributor cap
&erminal" should not be worn. t also should be checked for
e*cessive burning" carbon trace" looseness" or other damage.
Any wear or irregularity will result in e*cessive resistance to the
hightension spark. ake sure that the rotor +ts snugly on the
distributor shaft.
CONTACT "OINT !ISTRIBUTOR SER(ICE#$ n a contact point
distributor" there are two areas of concern the contact points
and the condenser. ,ad contact points cause a variety of
engine performance problems. &hese problems include high
speed missing" nostart problem" and many other ignition
troubles. Visually inspect the surfaces of the contact points to
determine their condition. @oints with burned and pitted
contacts or with a worn rubbing block must be replaced.
Bowever" if the points look good" point resistance should be
measured. &urn the engine over until the points are closed and
then use an ohmmeter to connect the meter to the primary
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point lead and to ground. f resistance reading is too high" the
points are burned and must be replaced.
A faulty condenser may leak #allow some dc current to ow to
ground%" be shorted #direct electrical connection to ground%" or
be opened #broken lead wire to the condenser foils%. f the
condenser is leaking or open" it will cause point arcing and
burning. f the condenser is shorted" primary current will ow to
ground and the engine will 2
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electrical impulses to the 85>. f the distributor fails to produce
these electrical impulses properly" the ignition system can 'uit
functioning.
A faulty pickup coil will produce a wide range of engine
troubles" such as stalling" oss
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Iith one tooth of the trigger wheel pointing at the pickup coil"
slide the correct thickness nonmagnetic feeler gauge between
the trigger wheel and the pickup coil. ove the pickup coil in or
out until the correct air gap is set. &ighten the pickup coil
screws and doublecheck the air gap setting.
Ignition Ti4ing
&he ignition system must be timed so the sparks 9ump across
the spark plug gaps at e*actly the right time. Ad9usting the
distributor on the engine so that the spark occur sat this correct
time is called setting the ignition timing. &he ignition timing is
normally set at idle or a speed speci+ed by the engine
manufacturer. ,efore measuring engine timing" disconnect and
plug the vacuum advance hose going to the distributor. &his
action prevents the vacuum advance from functioning and
upsetting the readings. Ad9ustment is made by loosening the
distributor holddown screw and turning the distributor in its
mounting.
&urning the distributor housing against the distributor shaft
rotation A?VA258S &B8 &2=. &urning the distributor housing
with shaft rotation :8&A:?S &B8&2=. :efer to +gure -3.
Ihen the ignition timing is &
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ames blowing out of the open e*haust valve can overheat the
engine and crack the e*haust manifolds.
)igure 6-,8:
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r in
harmonic balance of the engine" or they may be on the engine
ywheel.
Iith the engine running" aim the ashing timing light at the
timing mark and
reference pointer. &he ashing timing light will make the mark
appear to stand still. f the timing mark and the pointer do not
line up" turn the distributor in its mounting until the timing
mark and pointer are aligned. &ighten the distributor holddown
screw.
LIG)TING CIRCUIT
Learning Objective: dentify lightingcircuit components" their
functions" and
maintenance procedures.
&he lighting circuit #+g. -6% includes the battery" vehicle
frame" all the lights" and various switches that control their use.
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&he lighting circuit is known as a singlewire system since it
uses the vehicle frame for the return.
&he complete lighting circuit of a vehicle can be broken down
into individual circuits" each having one or more lights and
switches. n each separate circuit" the lights are connected in
parallel" and the controlling switch is in series between the
group of lights and the battery. &he marker lights" for e*ample"
are connected in parallel and are controlled by a single switch.
n some installations" one switch controls the connections to the
battery" while a selector switch determines which of two circuits
is energized. &he headlights" with their high and low beams" are
an e*ample of this type of circuit.
n some instances" such as the courtesy lights" several switches
may be connected in parallel so that any switch may be used to
turn on the light.
Ihen a wiring diagram is being studied" all light circuits can be
traced from the
battery through the ammeter to the switch #or switches% to the
individual light.
LAM"S
Small gas+lled incandescent lamps with tungsten +laments are
used on automotive
and construction e'uipment #+g. --%. &he +laments supply
the light when su!cient
current is owing through them. &hey are designed to operate
on a low voltage current
of 1 or 6 volts" depending upon the voltage of the the vehicle
will be of the singleor
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doublecontact small onehalfcandlepower bulbs to large -0
candlepower bulbs. &he
greater the candlepower of the lamp" the more current it
re'uires when lighted. 7amps are identi+ed by a number on the
base. Ihen you replace a lamp in a vehicle" be sure the new
lamp is of the proper rating. &he lamps within 7amps are rated
as to size by the candlepower #luminous intensity% they
produce. &hey range from types with nibs to +t bayonet
sockets" as shown in lamp is also whiter than a conventional
lamp" which increases lighting ability.
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Higure -D.# A% Singlecontact bulbF #,% ?oublecontact bulb.
)igure 6-
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)igure 6-
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without operating the mechanical switch to get blackout marker
lights #including blackout taillights and stoplights% and blackout
driving lights. ,ut for stoplights for daylight driving or
headlights for ordinary night driving" you must +rst lift the
mechanical switch lever and then turn the main switch to the
right. &he au*iliary switch gives panel lights when the main
switch is in any of its
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)igure 6-8=.- )loor-mounted dimmer switch.
)igure 6-86.- %teering column mounted dimmer switch.
n one position" the high beams are turned on" and" in the other
position" the dimmer changes them to low beam.Ai4ing )ead3ig/t&
&he headlights can be aimed using a mechanical aimer or a
wall screen. 8ither method assures that the headlight beams
point in the direction speci+ed by the vehicle manufacturer.
Beadlights that are aime d too high can blind oncoming
vehicles. Beadlights that are aimed too low or to one side will
reduce the operatorPs visibility.&o ensure that the headlights
are properly aimed" you should have a half a tank of fuel" the
correct tire pressure" and only the spare tire and 9ack in the
vehicle. Some manufacturers recommend that someone sit in
the operator and passenger seats while aiming the lights.
B8A?7=B& A8:S are a device for pointing the vehicle
headlights in a speci+ed position. &hey may be permanently
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installed on a track or may be portable. Some re'uire a level
oor" and others have internal levelling mechanisms to allow
for uneven shop oors. &o use the aimer" follow the instructions
for the speci+c type of e'uipment.
&he B8A?7=B& A2= S5:882 is a series of measured lines
marked on a shop wall or on a framed easel for aiming the
headlights of a vehicle. &he screen should beno less than 10
feet wide and 6 inches high. Ihen it is mounted on an easel
with casters" the screen should be no more than 1 inches from
the oor. &o comply with regulations of most localities" you
should place the screen - feet ahead of the vehicle.
)igure 6-8.- Accepted +eam pattern for aiming passenger vehicle headlights
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Higure D6. Accepted beam pattern for a fourheadlight
&%&te4#
BLAC'OUT LIG)TS
,lackout lighting is a re'uirement for certain combat
operations. &he purposes of blackout lighting are as follows4
&o provide the vehicle operator with su!cient light to operate
the vehicle in total darkness
to provide the vehicle operator with su!cient light to operate
vehicle in total darkness
&o provide minimum lighting to show vehicle position to a
leading or trailing vehicle when illumination must be restricted
to a level not visible to a distant enemy
&he three types of blackout lighting are as follows4
&he ,7A5Q& ?:V2= 7=B& #+g. D-% is designed to provide
a white light of
- to -0 candlepower at a distance of 10 feet directly in front of
the light. &he light is shielded so that the top of the low beam is
directed not less than degrees below the horizon. &he beam
distribution on a level road at 100 feet from the light is 30 feet
wide.
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)igure 6-8
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)igure 6-88.- Blac2out stop> taillight and mar2er light.
)igure 6-89.- ?ilitar, composite light.
,lackout lighting control switches are designed to prevent the
service lighting from being turned on accidentally. &heir
operation is described in the Beadlight Switch section of this
&:AA2.
TURN$SIGNAL SYSTEMS
Vehicles that operate on any public road must be e'uipped with
turn signals. &hese signals indicate a left or right turn by
providing a ashing light signal at the rear and front of the
vehicle.
&he turnsignal switch is located on the steering column #+g.
DE%. t is designed to shut o( automatically after the turn is
completed by the action of the cancelling cam.
Higure DE. &ypical turnsignal switch.
A wiring diagram for a typical turnsignal system is shown in
+gure DK. A common design for a turnsignal system is to use
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the same rear light for both the stop and turn signals. &his
somewhat complicates the design of the switch in that the
stoplight circuit must pass through the turnsignal switch. Ihen
the turnsignal switch is turned o(" it must pass stoplight
current to the rear lights. As a left or right turn signal is
selected" the stoplight circuit is open and the turnsignal circuit
is closed to the respective rear light.
&he turn signal asher unit #+g. /0% creates the ashing of
the turn signal lights. t consists basically of a bimetallic #two
dissimilar metals bonded together% strip wrapped in a wire coil.
&he bimetallic strip serves as one of the contact points.
Ihen the turn signals are actuated" current ows into the
asher +rst through the heating coil to the bimetallic strip"
then through the contact points" then out of the asher" where
the circuit is completed through the turnsignal light. &his
se'uence of events will repeat a few times a second" causing a
steady ashing of the turn signals.
BAC'U" LIG)T SYSTEM
&he backup light system provides visibility to the rear of the
vehicle at night and a warning to the e'uipped vehicles is
combined with the neutral safety switch pedestrians" whenever
the vehicle is shifted into reverse. &he backup light system has
a fuse" gearshiftor transmissionmounted switch" two backup
lights" and wiring to connect these components.
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)igure 6-8;.- T,pical turn-signal wiring diagram.
)igure 6-9.- Turn signal flasher.
&he backup light switch closes the light circuit when the
transmission is shifted into reverse. &he most common backup
light switch con+gurations are as follows4
&he backup light switch mounted on the transmission and
operated by the shift lever.
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&he backup light switch mounted on the steering column and
operated by the gearshift linkage.
&he transmissionor gearshiftmounted backup light switch on
many automatic
&ransmission.
TEM"ERATURE GAUGE
&he temperature gauge is a very important indicator in
construction and automotive e'uipment. &he most common
uses are to indicate engine coolant" transmission" di(erential
oil" and hydraulic system temperature. ?epending on the type
of e'uipment" the gauge may be mechanical" electric" or a
warning light.
&he 8785&:5 =A>=8 may be the thermostatic or magnetic
type" as described
previously. &he sending unit #+g. E3% that is used varies"
depending upon
application.
1. &he sending unit that is used with the thermostatic gauge
consists of two bimetallic strips" each having a contact
point.
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indicator light previously discussed.
)igure 6-6.- T,pes of sending units for pressure gauges
)igure 6-.- T,pes of temperature gauge sending units.
*IN!S)IEL! *I"ERS
&he windshield wiper system is one of the most importantsafety factors on any piece of e'uipment. A typical electricwindshield wiper system consists of a switch" motor assembly"wiper linkage and arms" and wiper blades. &he description ofthe components is as follows4
&he I2?SB87? I@8: SI&5B is a multi position switch"
which may contain a rheostat. 8ach switch position provides for
di(erent wiping speeds. &he rheostat" if provided" operates the
delay mode for a slow wiping action. &his permits the operator
to select a delayed wipe from every 3 to 0 seconds.
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A relay is fre'uently used to complete the circuit between the
battery voltage and the wiper motor.
&he I@8:
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)igure 6-;.- &iring diagram s,m+ols.
Conclusion
ence !or t"is pro#ect $e stu%ie% an% un%erstoo% a&out t"e
Electrical $or' %one in automo&ile section(