Manual Drivetrains and Axles Fourth Edition

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start
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OBJECTIVES
After studying Chapter 36, the reader should be
able to

• Prepare for ASE Electrical/Electronic Systems
  (A6) certification test content area A
  (General Electrical/Electronics System
  Diagnosis).
• Draw the symbols used on schematics.
• Discuss the various methods that can be use to
  locate a short circuit.
• List the electrical troubleshooting diagnosis
  steps.

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KEY TERMS

• double-pole, double-throw switch (DPDT)
  double-pole, single-throw switch (DPST)
• gauss gauge momentary switch
• normally closed (N.C.) normally open (N.O.)
  poles
• relay short circuit single-pole, double-throw
  switch (SPDT) single-pole, single-throw switch
  (SPST)
• terminal throws tone generator tester
  wiring schematic

4
WIRING SCHEMATICS

• Manufacturers service manuals include wiring
  schematics of all the electrical circuits of a
  vehicle. A wiring schematic, called a diagram,
  shows electrical components and wiring using
  symbols and lines to represent components and
  wires.A typical wiring schematic may include
  all of the circuits combined on several large
  fold-out sheets, or they may be broken down to
  show individual circuits.All circuit schematics
  or diagrams include the power-side wiring of the
  circuit and all splices, connectors, electrical
  components, and ground return paths.Gauge and
  color of wiring are included on most wiring
  diagrams.

Continued
5
Figure 361 The center wire is a solid color
wire, meaning that the wire has no other
identifying tracer or stripe color. The two end
wires could be labeled BRN/WHT, indicating a
brown wire with a white tracer or stripe.

• Circuit Information Many wiring schematics
  include numbers and letters near components and
  wires that may confuse readersof the schematic.
  Most letters used near or on a wire identify the
  color or colors of the wire. The first coloror
  color abbreviation is the color of
  theinsulation, the second color is the colorof
  the strip or tracer on the base color.

Chart on Page 370 of your textbook.
Continued
6
Figure 362Typical section of a wiring diagram.
Notice that the wire color changes at connection
C210. The .8 represents the metric wire size in
square millimeters.

• Shown here is a rear side-marker bulb circuit
  diagram where .8 indicates the metric wire
  gauge size in square millimeters (mm2)and PPL
  indicates a solid purple wire.

The diagram also shows the color of the wire
changes at C210. This stands for connector 210
and is used for reference purposes, and can vary
depending on the manufacturer.
The color change from purple (PPL) to purple with
a white tracer (PPL/WHT) is not important except
to know where the wire changes color in the
circuit. Wire gauge remained the same on both
sides of the connection
Continued
7
Figure 363 This figure shows typical electrical
and electronic symbols used in automotive wiring
and circuit diagrams.

• Electrical and electronic symbols used in wiring
  circuit diagrams.

See the chart on Page 371 of your textbook.
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Wiring diagrams indicate connections by symbols
that look like arrows.Do not read these arrows
as pointers showing the direction of
current flow. Also observe that the power side
(positive side) of the circuit is usually the
female end of the connector. If a connector
becomes disconnected, it will be difficult for
the circuit to become shorted to ground or to
another circuit because the wire is recessed
inside the connector.
Read The Arrows
Figure 364In this typical connector, note that
the positive terminal is usually a female
connector.
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SCHEMATIC SYMBOLS

• Schematic drawings replace photos, or line
  drawings of actual components with a symbol that
  represents the actual component

Battery The plates of a battery are represented
by long and short lines. The longer line
represents the positive plate of a battery and
the shorter line represents the negative plate of
the battery. Each pair of short and long lines
represents one cell of a battery.
Figure 365 The symbol for a battery. The
positive plate of a battery is represented by the
longer line and the negative plate by the shorter
line. The voltage of the battery is usually
stated next to the symbol.
Continued
10
Figure 366The ground symbol on the left
represents earth ground. The ground symbol on the
right represents a chassis ground.

• Because each cell of a typical automotive
  lead-acid battery has 2.1 volts, a battery symbol
  showing a 12-volt battery should have six pairs
  of lines. However, most symbols simply use two or
  three pairs of long and short lines and list
  battery voltage next to the symbol. The
  positive terminal of the battery is indicated
  with a plus sign (), representing the positive
  post of the battery, placed next to the long line
  of the end cell. The negative (ground) terminal
  is represented by a negative sign () and is
  placed next to the shorter cell line.

Continued
11

• Wiring Electrical wiring is shown as straight
  lines with a few numbers and/or letters to
  indicate

• Wire sizeThis can be either AWG, such as 18
  gauge or in square millimeters, such as 0.8.
• Circuit numbersEach wire in part of a circuit is
  labeled with the circuit number to help the
  service tech trace the wiring and allows for an
  explanation of how the circuit is supposed to
  work.
• Wire colorMost schematics also indicate an
  abbreviation for the color of the wire and place
  it next to the wire. Many wires have two colors
  a solid color and a stripe color. In this case,
  the solid color is listed, and then a dark slash
  (/) and the color of the stripe is listed. For
  example, red/wht would indicate a red wire with a
  white tracer.See Figure 367.

Continued
12
Figure 367 Starting at the top, the wire from
the ignition switch is attached to terminal B of
connector C2, the wire is 0.5 mm 2 (20-gauge AWG)
and is yellow. The circuit marker is 5. The wire
enters connector C202 at terminal B3.
Continued
13

• TerminalsThe metal part attached at the end of a
  wire is called a terminal. A symbol for a
  terminal is shown in Figure 368.
• Wire connectionsWhen two wires are electrically
  connected, the junction is shown with a black
  dot. See Figure 369.
• When two wires cross in a schematic that are not
  electrically connected, one of the wires is shown
  as going over the other wire and does not
  connect. See Figure 3610.
• ConnectorsAn electrical connector is a plastic
  part that contains one or more terminals. While
  the terminals provide the electrical connection
  in a circuit, it is the plastic connector that
  keeps the terminals together mechanically.

Continued
14
Figure 368The electrical terminals are usually
labeled with a letter, as shown on this cooling
fan motor.
Figure 369Two wires that cross at the dot
indicate that the two are electrically connected.
Figure 3610Wires that cross, but do not
electrically contact each other, are shown with
one wire bridging over the other.
Continued
15

• Connections are usually labeled with a C and
  three numbers which indicate the general location
  of the connector.Connector numbers represent
  the general area of the vehicle.

Even-numbered connectors are on the right
(passenger side) of the vehicle, odd-numbered
connectors on the left (drivers side).
100 to 199 Under the hood 200 to 299 Under the
dash 300 to 399 Passenger compartment 400 to 499
Rear package or trunk area
500 to 599 Left-front door 600 to 699 Right-front
door 700 to 799 Left-rear door 800 to 899
Right-rear door
Continued
16
Figure 3611Connectors (C), grounds (G), and
splices (S) are followed by a number, generally
indicating the location in the vehicle. For
example, G209 is a ground connection located
under the dash.
C-102 is a connector located under the hood
(between 100 and 199) on the right side of the
vehicle (even number 102).
Continued
17
Figure 3612 The ground for the battery is
labeled G305 indicating the ground connector is
located in the passenger compartment of the
vehicle. The ground wire is black (BLK), the
circuit number is 50, and the wire is 32 mm 2
(2-gauge AWG).

• Grounds and SplicesGrounds and splices are also
  labeled using the same general format as
  connectors.

A ground located under thedash on the drivers
sidecould be labeled G-201(G means ground).A
splice indication is an S followed by three
numbers,such as S-301.
Continued
18
Figure 3613 The symbol for light bulbs shows
the filament inside a circle, which represents
the glass ampoule of the bulb.

• Electrical Components Most components have their
  own unique symbol that shows basic function or
  parts.

• BulbsLight bulbs usually use a filament, which
  heats and then gives off light when electrical
  current flows. The symbol used for a light bulb
  shows a circle with a filament inside. A
  dual-filament bulb, such as is used for
  taillights and brake light/turn signals, is shown
  with two filaments.

Continued
19

• Electric Motors An electric motor symbol shows a
  circle with the letter M in the center and two
  electrical connections, one to the top and one at
  the bottom. See Figure 3614 for an example of a
  cooling fan motor.Resistors Usually part of
  another component, the symbol does appear on many
  schematics and wiring diagrams. A resistor symbol
  is a jagged line representing resistance to
  current flow. If the resistor is variable, such
  as a Thermistor, an arrow is shown running
  through the symbol of a fixed resistor.A
  potentiometer is a three-wire variable resistor
  and it is shown with an arrow pointing toward the
  resistance part of a fixed resistor.See Figure
  3615

Continued
20
Figure 3614 An electric motor symbol shows a
circle with the letter M in the center and two
black sections that represent the brushes of the
motor. This symbol is used even though the motor
is a cross-flow design.
Figure 3615Resistor symbols vary depending on
the type of resistor.
Continued
21
Figure 3616 A rheostat uses just two wiresone
is connected to a voltage source and the other is
attached to the movable arm.

• A two-wire rheostat is usually shown as part of
  another unit, such as a fuel level sending unit.

Continued
22

• Capacitors Usually part of an electronic
  component and not a replaceable component. Older
  vehicles used capacitors to reduce radio
  interference. They were installed inside
  alternators or attached to wiring connectors. See
  Figure 3617.Electric Heated Unit Electric
  grid-type rear window defoggers and cigarette
  lighters are shown in a square box-type
  symbol.Figure 3618.Boxed Components If a
  component is shown in a box using a solid line,
  the box is the entire component. If a box uses
  dashed lines, it represents a part of a
  component. A commonly used dashed-line box is a
  fuse panel. Often, just one or two fuses are
  shown in a dashed-line box, meaning the fuse
  panel has more fuses than shown. See Figures
  3619 and 3620.

Continued
23
Figure 3617Symbols used to represent
capacitors. If one of the lines is curved, this
indicates that the capacitor being used has a
polarity, while the one without a curved line can
be installed in the circuit without concern about
polarity.
Figure 3618The grid-like symbol represents an
electrically heated element.
Continued
24
Figure 3619A dashed outline represents a
portion (part) of a component.
Figure 3620A solid box representsan entire
component.
Continued
25

• Separate Replaceable Part Often components shown
  on a schematic cannot be replaced but are part of
  a complete assembly. On a schematic of GM
  vehicles, the following is shown

• If a part name is underlined, it is a replaceable
  part.
• If a part is not underlined, it is not available
  as a replaceable part, but is rather included
  with other components shown and sold as an
  assembly.
• If the case itself is grounded,the ground symbol
  is attachedto the component as shown.

Figure 3621This symbol represents a component
that is case grounded.
Continued
26

• Switches Electrical switches are drawn on a
  wiring diagram in their normal position. This can
  be one of two possible positions

• Normally open The switch is not connected to a
  terminal and no current flows in this position.
  This type of switch is labeled N.O.
• Normally closed The switch is electrically
  connected to a con-tact and current will flow
  through the switch. This type of switch is
  labeled N.C.

NOTE All switches are shown on schematics in
their normal position. This means that the
headlight switch will be shown normally off, as
are most other switches and controls.
Continued
27

• Other switches can use more than two
  contacts.The poles refer to the number of
  circuits completed by the switch and the throws
  refer to the number of output circuits. A
  single-pole, single-throw (SPST) switch has only
  two positionson or off.A single-pole,
  double-throw (SPDT) switch has three
  terminalsone wire in and two wires out. A
  headlight dimmer switch is an example of a
  typical SPDT switch. In one position, the current
  flows to the low-filament headlight in the
  other, the current flows to the high-filament
  headlight.There are also double-pole,
  single-throw (DPST) switches and double-pole,
  double-throw (DPDT) switches.See Figure 3622.

Continued
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Figure 3622 (a) A symbol for a single-pole,
single-throw (SPST) switch. This type of switch
is normally open (N.O.) because nothing is
connected to the terminal that the switch is
contacting in its normal position. (b) A
single-pole, double-throw (SPDT) swtich has three
terminals. (c) A double-pole, single-throw (DPST)
swtch has two positions (off and on) and can
control two separate circuits. (d) A double-pole,
double-throw (DPDT) switch has six
terminalsthree for each pole. Note c and d
also show a dotted line between the two arms
indicating that they are mechanically connected.
(a)
(b)
(c)
(d)
Continued
29

• Another type of switch that is used on most
  vehicles is called a momentary switch. Usually
  used to send a voltage signal to a module or
  controller to request a device be turned on or
  off.The switch just makes momentary contact and
  returns to the open position. The symbol that
  represents a momentary switch uses two dots for
  the contact with a switch above them.A
  momentary switch, for example, can be used to
  lock or unlock a door or to turn the air
  conditioning on or off. If the device is
  currently operating, the signal from the
  momentary switch will turn it off, and if it is
  off, the switch will signal the module to turn it
  on.An advantage of momentary switches is they
  can be very lightweight and small. Most
  momentary switches use a membrane constructed of
  foil and plastic.

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RELAY TERMINAL IDENTIFICATION

• A relay is a magnetic switch that uses a movable
  armature to control a heavy electrical load by
  using a low-amperage electrical switch. Most
  automotive relays adhere to common terminal
  identification.Relays are found in many
  circuits because they are capable of being
  controlled by computers, yet are able to handle
  enough current to power motors and accessories.
  See Figures 3623 and 3624.

Continued
31
Figure 3623 A relay uses a movable arm to
complete a circuit whenever there is a power at
terminal 86 and a ground at terminal 85. A
typical relay only requires about 1/10 ampere
through the relay coil. The movable arm then
closes the contacts (30 to 87) and can relay 30
amperes or more.
Continued
32
Figure 3624 A cross-sectional view of a typical
four-terminal relay. Current flowing through the
coil (terminals 86 and 85) causes the movable arm
(called the armature) to be drawn toward the coil
magnet. The contact points complete the
electrical circuit connected to terminals 30 and
87.
Continued
33
Figure 3625A typical relay showing the
schematic of the wiring in the relay. Terminals
30 and 87 are electrically connected when the
relay is energized.
Most relays use four or five terminals as follows

• A coil that provides magnetic pull to a movable
  armature (arm). The resistance of most relay
  coils ranges from 50 to 150 ohms, but is usually
  between 60 and 100 ohms. The International
  Standard Organization (ISO) identification of the
  coil terminals are 86 and 85. Terminal number
  86represents power to the relay coil85
  represents the ground side.

The relay coil can be controlled bysupplying
either power or groundto the relay coil winding.
Continued
34

• The higher amperage current flow through a relay
  flows through terminals 30 and 87 and often 87a.
  Terminal 30 is usually where power is applied.
  When the relay is at rest without power and
  ground to the coil, the armature inside the relay
  electrically connects terminals 30 and 87a if the
  relay has five terminals.When there is power at
  terminal 86 and a ground at terminal 85 of the
  relay, a magnetic field is created in the coil
  winding, which draws the armature of the relay
  toward the coil. The armature, when energized
  electrically, connects terminals 30 and 87.The
  maximum current through the relay is determined
  by the resistance of the circuit and relays are
  designed to safely handle the designed current
  flow.See Figures 3626 and 3627.

Continued
35
Figure 3627 A typical horn circuit. Note that
the relay contacts supply the heavy current to
operate the horn when the horn switch simply
completes a low current circuit to ground,
causing the relay contacts to close.
Figure 3626 All schematics are shown in their
normal, nonenergized position.
Continued
36
Figure 3628 When the relay or solenoid coil
current is turned off, the stored energy in the
coil forward biases the clamping diode and
effectively reduces voltage spike.

• Relay Voltage Spike Control Relays contain a
  coil and whenever power is removed, the magnetic
  field surrounding the coil collapses, creating a
  voltage to be induced in the coil winding.

This induced voltage can be as high as 100 volts
or more and can cause problems with other
electronic devices in the vehicle. The short
high-voltage surge can be heard as a pop in
the radio.
To reduce the induced voltage, some relays
contain a diode connected across the coil inthe
reverse bias direction.
Continued
37
Figure 3629A resistor used in parallel with the
coil windings is a commonly used spike reduction
method used in many relays.

• Most relays use a resistor connected in parallel
  with the coil winding. The use of a resistor,
  typically about 400 to 600 ohms, reduces the
  voltage spike by providing a path for the voltage
  created in the coil to flow back through the coil
  windings whenthe coil circuit is opened.

Continued
38
COMMON POWER OR GROUND

• Whenever diagnosing an electrical problem that
  affects more than one component or system, check
  the electrical schematic for a common power
  source or a common ground.

See Figure 3630 for an example where all of the
following lights are powered by one fuse (power
source).

• Under-hood light
• Inside lighted mirrors
• Dome light

• Left-side courtesy light
• Right-side courtesy light

For a customer complaint involving one or more of
the items listed, check the fuse and the common
part of the circuit that feeds all of affected
lights. Check for a common ground if several
components that seem unrelated are not
functioning correctly.
Continued
39
Figure 3630A typical wiring diagram showing
multiple switches and bulbs powered by one fuse.
Schematic on Page 376 of your textbook.
40
Often, a customer will notice just one fault
while other lights or systems may not be working
correctly. For example, a customer noticed that
the electric mirrors stopped working. The service
technician checked all electrical components in
the vehicle and discovered that the interior
lights were also not working.
Check Everything

• The interior lights were not mentioned by the
  customer as being a problem most likely because
  the driver only used the vehicle in daylight
  hours.

The service technician found the interior light
and power accessory fuse blown. Replacing the
fuse restored the proper operation of the
electric outside mirror and the interior lights.
However, what caused the fuse to blow? A visual
inspection of the dome light, next to the
electric sunroof, showed an area where a wire was
bare. Evidence was seen where the bare wire had
touched the metal roof, which could cause the
fuse to blow. The technician covered the bare
wire with a section of vacuum hose and then taped
the hose with electrical tape to complete the
repair.
41
Often the owners of vehicles, especially of
pickup trucks and sport utility vehicles (SUVs),
want to add additional electrical accessories or
lighting.It is tempting in these cases to
simply splice into an existing circuit.However,
whenever another circuit or component is added,
the current that flows through the newly added
component is also added to the current for the
original component. This additional current can
easily overload the fuse and wiring. Do not
simply install a larger-amperage fuse the wire
gauge size was not engineered for the additional
current and could overheat. The solution is a
relay, which uses a small coil to create a
magnetic field that causes a movable arm to
switch on a higher-current circuit.
Do It RightInstall a Relay - Part 1
42
Figure 3631 To add additional lighting, simply
tap into an existing light wire and connect a
relay. Whenever the existing light is turned on,
the coil of the relay is energized. The arm of
the relay then connects power from another
circuit (fuse) to the auxiliary lights without
overloading the existing light circuit.
The typical relay has 50 to 150 ohms (usually
60 to 100) of resistance and requires just 0.24
to 0.08 amp when connected to a 12-volt source.
This small additional current will not be enough
to overload the existing circuit.
Do It RightInstall a Relay - Part 2
43
USING SCHEMATICS FOR TROUBLESHOOTING

• Follow these steps when troubleshooting wiring
  problems.Step 1 Verify the malfunction. If,
  for example, the backup lights do not operate,
  make certain that the ignition is on (key on,
  engine off), with the gear selector in reverse,
  and check for operation of the backup
  lights.Step 2 Check everything that does or
  does not operate correctly. If the taillights are
  also failing to operate, the problem could be a
  loose or broken ground connection in the trunk
  area that is shared by both the backup lights and
  the taillights.Step 3 Check the fuse for the
  backup lights. See Figure 3632.

Continued
44
Figure 3632 Always check the simple things
first. Check the fuse for the circuit you are
testing. Maybe a fault in another circuit
controlled by the same fuse could have caused the
fuse to blow. Use a test light to check that both
sides of the fuse have voltage.

• Step 4 Check for voltage at the backup light
  socket. This can be done using a test light or a
  voltmeter.

If voltage is available at the socket, the
problem is either a defective bulb or a poor
ground at the socket or a ground wire connection
to the body or frame.
If no voltage is available at the socket, consult
a wiring diagram.
The wiring diagram should show all of the wiring
and components included in the circuit.
45
The common question is, where does a technician
start troubleshooting when using a wiring diagram
(schematic)?
Where to Start?

• If the circuit contains a relay, start your
  diagnosis at the relay.The entire circuit can be
  tested at the terminals of the relay.

HINT 1
The easiest first step is to locate the unit on
the schematic thatis not working at all or not
working correctly. Often a ground is used by
more than one component. Therefore, ensure that
everything else is working correctly. If not,
then the fault may lie at the common ground (or
power) connection..
HINT 2
a. Trace where the unit gets its ground
connection. b. Trace where the unit gets its
power connection.
HINT 3
Divide the circuit in half by locating a
connector or a part of thecircuit that can be
accessed easily. Then check for power andground
at this midpoint. This step could save you much
time.
46
LOCATING A SHORT CIRCUIT

• A short circuit usually blows a fuse, and a
  replacement fuse often also blows in the attempt
  to locate the source of the short circuit.A
  short circuit is an electrical connection to
  another wire or to ground before the current
  flows through some or all of the resistance in
  the circuit. A short-to-ground will always blow a
  fuse and usually involves a wire on the power
  side of the circuit coming in contact with
  metal.A short-to-voltage may or may not cause
  the fuse to blow and usually affects another
  circuit. Look for areas of heat or movement where
  two power wires could come in contact with each
  other.

Continued
47

• Several methods can be used to locate the short.
• Fuse Replacement Method Disconnect one component
  at a time and replace the fuse. If the new fuse
  blows, continue the process until the location of
  the short is determined. This method uses many
  fuses and is not a preferred method for finding a
  short circuit.Circuit Breaker Method Connect
  an automotive circuit breaker to contacts of the
  fuse holder with alligator clips. Circuit
  breakers are available that plug directly into
  the fuse panel, replacing a blade-type fuse. The
  circuit breaker will alternately open and close
  the circuit, protecting the wiring from damage
  while still providing current flow through the
  circuit.

NOTE A heavy-duty (HD) flasher can also be used
in place of a circuit breaker to open and close
the circuit. Wires and terminals must be made to
connect the flasher unit where the fuse normally
plugs in.
48

• All components in the defective circuit should be
  disconnected one at a time until the circuit
  breaker stops clicking. The unit that was
  disconnected and stopped the circuit breaker
  clicking is the unit causing the short circuit.
  If the circuit breaker continues to click with
  all circuit components unplugged, the problem is
  in the wiring from the fuse panel to any one of
  the units in the circuit. Test Light Method
  Remove the blown fuse and connect a test light to
  the terminals of the fuse holder. If there is a
  short, current will flow from the power side of
  the fuse holder through the test light to ground
  through the short circuit, and the test light
  will light.Unplug connectors or components
  protected by the fuse until the test light goes
  out.

Continued
49

• Ohmmeter Method The recommended method of finding
  a short.An ohmmeter indicates low ohms when
  connected to a short circuit. The correct
  procedure for locating a short using an ohmmeter

1. Connect one lead of an ohmmeter (set to a low
   scale) to a good clean metal ground and the other
   lead to the circuit side of the fuse holder.
2. The ohmmeter will read zero or almost zero ohms
   if the circuit is shorted.
3. Disconnect one component in the circuit at a time
   and watch the ohmmeter. If the ohmmeter reading
   goes to high ohms or infinity, the component just
   unplugged caused the short circuit.

CAUTION Connecting the lead to the power side
of the fuse holder will cause current flow
through and damage to the ohmmeter.
Continued
50

• Gauss Gauge Method A special pulsing circuit
  breaker (similar to a flasher unit) can be
  installed in place of the fuse. Current will flow
  through the circuit until the circuit breaker
  opens the circuit.As soon as the circuit
  breaker opens the circuit, it closes again. This
  on-and-off current flow creates a pulsing
  magnetic field around the wire carrying the
  current. A Gauss gauge is a handheld meter that
  responds to weak magnetic fields.This pulsing
  magnetic field will register on the Gauss gauge
  even through the metal body of the vehicle. A
  needle-type compass can also be used to observe
  the pulsing magnetic field.See Figures 3633
  and 3634.

Continued
51
Figure 3633 (a) After removing the blown fuse,
a pulsing circuit breaker is connected to the
terminals of the fuse. (b) The circuit breaker
causes current to flow, then stop, then flow
again, through the circuit up to the point of the
short-to-ground. By observing the Gauss gauge,
the location of the short is indicated near where
the needle stops moving due to the magnetic field
created by the flow of current through the wire.
Continued
52
Figure 3634 A Gauss gauge can be used to
determine the location of a short circuit even
behind a metal panel.

• A Gauss gauge is used to observe a pulsing
  magnetic field, which is indicated onthe gauge
  as needle movement.

Continued
53
Figure 3635 A tone generator-type tester used
to locate open circuits and circuits that are
shorted-to-ground. Included with this tester is a
transmitter (tone generator), receiver (probe),
and headphones for use in noisy shops.

• Electronic Tone Generator Tester An electronic
  tone generator tester can be used to locate a
  short-to-ground or an open circuit. Similar to
  test equipment used to test telephone and cable
  television lines, a tone generator tester
  generates a tone that can be heard through a
  receiver (probe).

The tone will be generated while there is a
continuous electrical path along the circuit. The
signal will stop if there is an open (break) or
short-to-ground in the circuit.
The windings in the solenoids and relays will
increase the strength of the signal in these
locations.
See Figures 3636 and 3637.
Continued
54
Figure 3636 To check for a short-to-ground
using a tone generator, connect the black
transmitter lead to a good chassis ground and the
red lead to the load side of the fuse terminal.
Turn the transmitter on and check for tone signal
with the receiver. Using a wiring diagram, follow
the strongest signal to the short-to-ground.
There will be no signal beyond the fault.
Continued
55
Figure 3637 To check for an open (break),
connect the red lead of the tone generator to the
load side of the fuse terminal and the black lead
to a good chassis ground. Turn on the transmitter
an then listen for the tone signal with the
receiver set in the open position. Using a wiring
diagram, follow the signal along the circuit
until the tone stops, indicating the location of
the open.
56
Electrical shorts are commonly caused either by
movement, which causes the insulation around the
wiring to be worn away, or by heat melting the
insulation. When checking for a short circuit,
first check the wiring that is susceptible to
heat, movement, and damage
Heat or Movement

1. Heat. Wiring near heat sources, such as the
   exhaust system, cigarette lighter, or
   generator.
2. Wire movement. Wiring that moves, such as in
   areas near the doors, trunk, or hood.
3. Damage. Wiring subject to mechanical injury,
   such as in the trunk, where heavy objects can
   move around and smash or damage wiring. This
   can also occur as a result of an accident or a
   previous repair.

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Intermittent electrical problems are common yet
difficult to locate. To help locate these
hard-to-find problems, try operating the circuit
and then start wiggling the wires and connections
that control the circuit.If in doubt where the
wiring goes, try moving all the wiring starting
at the battery. Pay particular attention to
wiring running near the battery or the windshield
washer container. Corrosion can cause wiring to
fail, and battery acid fumes and alcohol-based
windshield washer fluid can start or contribute
to the problem.If you notice any change in the
operation of the device being tested while
wiggling the wiring, look closer in the area you
were wiggling until the actual problem is located
and corrected.
Wiggle Test
58
ELECTRICAL TROUBLESHOOTING GUIDE

1. For a device to work, it must have power and
   ground.
2. If there is no power to a device, an open power
   side (blown fuse, etc.) is indicated.
3. If there is power on both sides of a device, an
   open ground is indicated.
4. If a fuse blows immediately, a grounded
   power-side wire is indicated.
5. Most electrical faults result from heat or
   movement.
6. Most noncomputer-controlled devices operate by
   opening and closing the power side of the circuit
   (power-side switch).
7. Most computer-controlled devices operate by
   opening and closing the ground side of the
   circuit (ground-side switch).

59
STEP-BY-STEP TROUBLESHOOTING PROCEDURE

• The following procedure has been field tested for
  many years and provides a step-by-step guide to
  follow when troubleshooting

1. Determine the customer concern (complaint) and
   get as much information as possible from the
   customer or service advisor.

1. When did the problem start?
2. Under what conditions does the problem occur?
3. Have there been any recent repairs to the vehicle
   which could have created the problem?

1. Verify the customers concern by actually
   observing the fault.

HINT Split the circuit help isolate the problem
and start at the relay.
60

1. Perform a thorough visual inspection and be sure
   to check everything that does and does not work.
2. Check for technical service bulletins (TSBs).
3. Check the factory service information and follow
   the troubleshooting procedure.

1. Determine how the circuit works
2. Determine which part of the circuit is good,
   based on what works and what does not work
3. Isolate the problem area

1. Determine the root cause and repair the vehicle.
2. Verify the repair and complete the repair order
   (R.O.) by listing the three Cs (complaint,
   cause, and correction).

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A customer complained that after driving for a
while, he got a static shock whenever the door
handle was grabbed when exiting the vehicle. The
customer thought that there must be an electrical
fault and that the shock was coming from the
vehicle itself. In a way, the shock was caused by
the vehicle, but it was not a fault.
Shocking Experience

• The service technician sprayed the cloth seats
  and carpet with an antistatic spray and the
  problem did not reoccur.

Obviously, a static charge was being created by
movement of the drivers clothing on the seats
and discharged when the driver touched the
metaldoor handle.
Figure 3638 Antistatic spray can be used to stop
customers from being shocked when they touch a
metal object like the door handle.
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SUMMARY

1. Most wiring diagrams include the wire color,
   circuit number, and wire gauge.
2. The number used to identify connectors, grounds,
   and splices usually indicates where they are
   located in the vehicle.
3. All switches and relays shown on a schematic are
   shown in their normal position either normally
   closed (N.C.) or normally open (N.O.).

Continued
63
SUMMARY
(cont.)

1. A short-to-voltage affects the power side of the
   circuit and usually involves more than one
   circuit.
2. A short-to-ground usually causes the fuse to blow
   and usually affects only one circuit.
3. Most electrical faults are a result of heat or
   movement.

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end