GMC ST 350 1988 Quick start guide

1988
LIGHT DUTY TRUCK
WIRING DIAGRAM
BOOKLET
ST-350-88

1
WIRING DIAGRAMS
All diagrams in this manual are based on the latest product information at the time of publication approval. The right is
reserved to make changes at any time without notice.
SUBJECT PAGE
Description.............................................................................................................................................................
Tracing Circuits..................................................................................................................................................
Basic Electric Circuits.........................................................................................................................................
Circuit Diagnosis................................................................................................................................................6
Abbreviation List................................................................................................................. . ................................ 7
Diagnostic Tools.................................................................................................................................................... 9
Wire Size Conversion Table...............................................................................................................................11
On-Vehicle Service................................................................................................................................................11
Circuit Maintenance and Repair..........................................................................................................................11
Weather Pack Connectors...................................................................................................................................1
Metri-Pack Connectors.........................................................................................................................................1
Wiring Repair......................................................................................................................................................14
Special Tools..........................................................................................................................................................15
VEHICLE SECTION
C/K Models............................................................................................................................................................A-1
G Van.....................................................................................................................................................................B-1
S/T Models............................................................................................................................................................C-1
R/V Models............................................................................................................................................................D-1
P Chassis...............................................................................................................................................................E-1
M Van.....................................................................................................................................................................F-1
WIRING DIAGRAMS
DESCRIPTION
9A 0.5 BRN
WIRE
CIRCUIT
NUMBER
WIRE SIZE
IN SQ. MM.
I
COLOR OF WIRE
BLK .................. Black
BRN ................ Brown
CHK ................ Check
CR .................... Cross
GRN ................ Green
NAT .............. Natural
SGL ................ Single
ORN .............. Orange
GR ...................... Gray
INSULATION
PPL ................ Purple
TR .................... Tracer
YEL ................ Yellow
II .................... Parallel
WHT ................ White
BLU .................... Blue
STR .................. Stripe
PNK .................... Pink
DK ......................Dark
F- 5975
Figure 1—Wire Coding
• The diagrams are to be traced from the source of
electricity (the battery positive post) to ground. The
ground may be a chassis ground on a certain com
ponent (such as an alternator or a starter), or a wire
from a component to a chassis or frame ground
(such as used on the electronic control module and
instrument panel). All grounds are connected to the
negative battery post through body and/or engine
ground wires and straps.
• Many times the source of the electricity is shown as
the ignition switch or the fuse block. This is done to
eliminate the confusion that would occur if the entire
power distribution was shown in each circuit. For a
detailed outline of the power to the ignition switch or
the fuse block, refer to the power distribution circuit.
• The ground portion of the circuit (usually circuit 15
or 151) may be shown entirely, or it may refer to the
ground distribution circuit in order to avoid confu
sion of listing all the grounds in one splice on a sin
gle page.
• For ease of diagnosis, all splices and grounds are
identified by number, and all the wires in a common
splice or ground are identified by circuit number,
size (in mm) and color. Each component or circuit
common to s spliced wire is called out by the page
number of that circuit. This will help identify and di
agnose multiple electrical problems that could occur
in a truck.
• All connectors are shown with their part numbers to
save time when ordering these parts.
• Switches are shown in their at rest positions, unless
otherwise marked.
TRACING CIRCUITS
Figures 1 through 3 are examples of how the wiring
diagrams are laid out, and will be referred to, throughout
this description.
In order to trace a circuit on these diagrams, start from
the source, the battery. In figure 2, the battery positive
circuit is a 19. mm black wire. This wire runs from the
battery to the starter motor, and supplies power to the
starter motor post.
Once you have determined the source of power to your
component, from the Power Distribution Circuit (figure 2),
then refer to the individual circuit you are working on for
more detail about that circuit. (Figure 3 shows the starting
circuit).
In figure 3, the starter motor circuit is shown. This circuit
shows the battery feed coming from the Power
Distribution page. The cable comes from the battery to
the starter positive post. At the starter post, other circuits
such as the generator, ignition switch, and electronic
control module are fed.
When the ignition switch is in the start position, power
flows from circuit #2 through the switch, to circuit #6.
Circuit #6 goes through the clutch switch with an
automatic transmission. At the clutch switch the circuit is
opened, unless the clutch is depressed.
At the solenoid the current flowing from circuit #6,
closes the solenoid, allowing current to flow from the
battery at circuit #1 to the starter motor. The current
flowing to the starter motor, causes the starter motor to
spin.
BASIC ELECTRICAL CIRCUITS
An electrical circuit starts from a supply of electricity
back to a load and then conducts the electricity back to
the supply of electricity. There should be a device to open
and close the circuit, and a protective device to open the
circuit in case too much current is drawn into the circuit by
an overload condition. Electrical circuits can be set up as
series circuits, parallel circuits or series/parallel circuits.
The circuits in trucks are usually parallel circuits.

WIRING DIAGRAMS 3
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Figure —Power Distribution
F-0598
WIRING DIAGRAMS 4
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F-05983
Figure 3—Starter System

WIRING DIAGRAMS 5
1. Battery
. Parallel Circuit
3. Load
4. Switch
5. Series Circuit
3
B- 349
Figure 4—Basic Circuits
SERIES CIRCUITS (Figure 4 and 5)
In a series circuit, the electrical devices are connected
together to form one current path to and from the power
supply. In a series circuit the same current flows through
all of the devices.
PARALLEL CIRCUITS (Figure 5)
In a parallel circuit, the electrical devices are conected
to form more than one current path to and from the power
supply. In a parallel circuit the supply voltage is the same
in each current path.
SERIES/PARALLEL CIRCUIT (Figure 5)
A series/parallel circuit consists of a single current path
circuit and a circuit with more than one current path to
and from the voltage supply.
CIRCUIT COMPONENTS (Figure 6)
The usual circuit path starts at the power supply which
is the battery/generator system. Next in the circuits is the
circuit protection component which can be a fusible link, a
fuse, or a circuit breaker. Then the circuit goes to the
circuit controller which can be a switch or a relay. From
the circuit controller the circuit goes into the circuit load.
The circuit load can be one light or many lights in parallel,
an electric motor or a solenoid. After the electricity has
passed through the load it must return to the power
supply via the ground path. The ground path can be a
wire in the harness or it could be through the load
housing into the body or frame, thus returning the
electricity to the power supply. The body and frame are
connected by flexible ground straps.
Figure 5—Series/Parallel Circuits
FUSIBLE LINK
A fusible link is a section of wire that is usually four
gage sizes smaller than the circuit it protects. A special
insulation is used that swells when heated by the wire.
Fusible links are usually found in the engine compartment
harnesses. The function of the fusible link is to melt open
when an overload occurs, thus preventing any damage to
the circuit.
Figure 6—Circuit Components
WIRING DIAGRAMS 6
FUSES (Figure 6)
The most common protector in the vehicle circuit is a
fuse. A fuse consists of a fine wire or strip of metal inside
a glass tube or plastic housing. The strip melts and
interrupts the flow of current in the circuit when there is an
overload caused by an unwanted short or ground. The
fuse is designed to melt before the wiring or electrical
components in a circuit can be damaged. Naturally, the
cause must be located and corrected before the fuse is
replaced or the new fuse will also blow.
Since different circuits handle different amounts of
current, fuses of various ratings are used. Fuses are rated
in amperes. Be sure to replace a blown fuse with a fuse of
the connecting rating.
CIRCUIT CONTROLLERS (Figure 7)
Circuit controllers consist of switches or relays.
Switches are usually operated by a mechanical means
such as a hand or lever. Switches are usually at the
beginning of a circuit but can be used to control a ground
path. For example the switch controlling the headlights is
at the power end of the circuit while the door switch
controlling the domelight completes the ground path.
Relays are remotely controlled switches. They are used
in high current circuits and in circuits controlled by
sensors.
Relays are designed so that a small current circuit will
be able to control a large current circuit.
CIRCUIT BREAKERS (Figure 7)
Circuit breakers are another form of circuit protector.
There are two types of circuit breakers; automatic reset
and remote reset.
The automatic reset breaker opens when excess
current heats a bimetallic strip, causing the strip to bend
and open a set of contacts. Then the strip cools and
closes the contacts. So the circuit breaker opens and
closes until the excess current condition is corrected or
the circuit is disconnected from the power supply.
The remote reset circuit breaker has a heating wire
wound around the bimetallic strip. When an excess
current happens, the strip heats, bends, and opens the
contacts. Then a small current flows through the heating
wire, keeping the strip hot and the contacts open. This
type of breaker will stay open until either the power supply
is disconnected from the circuit or the breaker is removed
from the circuit. Then the breaker can cool and reset.
CIRCUIT LOADS (Figure 7)
Circuit loads are the components that use most of the
energy in circuit. The energy converts to motion, light, or
heat. Lights, motors, and engine heaters are the most
common loads in circuits.
CIRCUIT DIAGNOSIS
A clear understanding of the circuit and a wiring
diagram are needed for effective diagnosis. Use a logical
sequence of testing to find the trouble. Use the diagnostic
tools. After the trouble is fixed, make sure the circuit
works correctly.
CIRCUIT MALFUNCTIONS
There are three electrical conditions that can cause a
nonworking circuit; an “Open Circuit” , a “ Short Circuit” ,
or a “Grounded Circuit.”
OPEN CIRCUIT (Figure 8)
An open circuit occurs whenever there is a break in the
circuit. The break can be corrosion at the connector, a
wire broken off in a device, or a wire that burned open
from too much current.
SHORT CIRCUIT (Figure 9)
A short circuit happens when the current bypasses part
of the normal circuit. This bypassing is usually caused by
wires touching, salt water in or on a device such as a
switch or a connector or solder melting and bridging
conductors in a device.

WIRING DIAGRAMS 7
GROUNDED CIRCUIT (Figure 10)
A ground circuit is like a short circuit but the current
flows directly into a ground circuit that is not part of the
original circuit. This may be caused by a wire rubbing
against the frame or body. Sometimes a wire will break
and fall against metal that is connected electrically to the
ground side of the power supply. A grounded circuit may
also be caused by deposits of oil, dirt and moisture
around connections or terminals, which provide a good
path to ground.
ABBREVIATION LIST
The following is a list of abbreviations used in the wiring
diagrams. The abbreviations have been developed in
such a way that their meaning should be clear.
Use this page as a reference to determine the meaning
of an abbreviation if necessary.
A—Ampere
A/C—Air Conditioner
ACC—Accessory
A.I.R.—Air Injection Reaction
AIR/COND—Air Conditioner
ALDL—Assembly Line Diagnostic Link
ALT—Alternator
AMP—Ampere
ANTI—Anticipate
ASM—Assembly
ASS’Y—Assembly
AUD—Audio
AUTO—Automatic
AUX—Auxiliary
BAT—Battery
BATT—Battery
BI-LEV—Bi-Level
BLK—Black
BLT— Belt
BLU—Blue
BOT—Bottom
BRK—Brake
BRN—Brown
BU—Backup
BUZZ—Buzzer
CIR/BRK—Circuit Breaker
CIRC—Circuit
CLSTR—Cluster
CNTL—Control
COMP—Compartment
COMP—Compressor
CONN—Connector
CONV— Convenience
CTS Y—Courtesy
CYL—Cylinder
DK—Dark
DIAG—Diagnostic
DIM—Dimmer
DIR—Directional
DISC—Discrete
DIST—Distributor
DIV—Diverter
DM—Dome
DR—Door
ECM—Electronic Control Module
WIRING DIAGRAMS 8
EFE— Early Fuel Evaporation
EGR—Exhaust Gas Recirculation
ELEC—Electric
ELEC—Electronic
CNTRL—Control
MOD—Module
ENG—Engine
EPR—Exhaust Pressure Regulator
ESC—Electronic Spark Control
EST—Electronic Spark Timing
EVRV—Electronic Vacuum Regulator Valve
EXC—Except
F-PUMP—Fuel Pump
FLASH—Flasher
FRT—Front
4WD—Four Wheel Drive
GEN—Generator
GRA—Gray
GRD—Ground
GRN—Green
HAND—Handling
HAZ—Hazard
HD—Heavy Duty
HD LP—Headlamp
HEI—High Energy Ignition
HI—High
HTR— Heater
IAC—Idler Air Control
IGN—Ignition
ILLUM—Illumination
l/P—Instrument Panel
INC—Increased
IND—Indicator
INJ—Injector
INST PNL—Instrument Panel
INTER—Interior
LD—Light Duty
LH—Left Hand
LO—Low
LP—Lamp
LPS—Lamps
LT—Light
LTR—Lighter
M—Motor
MAN—Manual
MAP—Manifold Absolute Pressure
MAX—Maximum
MED—Medium
MRKR—Marker
MULT—Multiple
NAT—Natural
NEUT—Neutral
NO—Normally Open
NC—Normally Closed
ORN—Orange
PK— Park
PLR—Puller
PNK—Pink
PNL—Panel
PPL—Purple
PRESS—Pressure
PWR—Power
RCVR—Receiver
REF—Reference
RESIST—Resistance
RH—Right Hand
RPO—Regular Production Option
SEN—Senser
SEND—Sender
SIG—Signal
SIL—Silver
SKT—Socket
SOL—Solenoid
SPEEDO—Speedometer
STR—Stripe
SW—Switch
TACH—Tachometer
TBI—Throttle Body Injection
TCC—Torque Converter Clutch
TEMP—Temperature
T/L—Tail Lamp
TRANS—Transmission
TYP—Typical
V—Volt
VAC—Vacuum
VLV—Valve
VSS—Vehicle Speed Sensor
W/—With
W/O—Without
W/S—Windshield
W WASHER—Window Washer
WDO—Window
WHT—White
WRG—Wiring
YEL—Yellow

WIRING DIAGRAMS 9
DIAGNOSTIC TOOLS
UNPOWEREO TEST LIGHT (Figure 1 )
This tool consists of a 12 volt light with leads. The ends
of the leads usually have alligator clamps, but various
kinds of probes, terminal spades, and special connectors
are used also.
The unpowered test light is used on an open circuit.
One lead of the test light is grounded and the other lead is
moved around the circuit to find the open. Depending on
the physical layout of the circuit, sometimes it will be
easier to start at the power supply and other times it is
easier to start at the circuit load or ground circuit.
POWERED TEST LIGHT (Figure 11)
This light is a pencil shaped unit with a self contained
battery, a 1.5 volt light bulb, a sharp probe and a ground
lead fitted with an alligator clip.
This test light is used mainly for testing components
that are disconnected from the vehicle power supply. The
power test light is also useful for testing suspected high
resistance points in a circuit such as connectors and
ground circuits that are corroded or loose.
JUMPER
The jumper is usually a long wire with alligator clamps.
A version of the jumper has a fuse holder in it with a 1
Amp fuse. This will prevent damaging the circuit if the
jumper is connected in the wrong way.
The jumper is used to locate opens in a circuit. One
end of the jumper is attached to a power source and then
the other end is attached to the load in the circuit, i.e.;
light, motor. If the load works, try “jumping” to circuit
points that are progressively closer to the power supply.
When the circuit load stops working, the open has been
located.
The jumper is also used to test components in the
circuit such as connectors, switches, and suspected high
resistance points.
NOTICE: The following instruments: Ammeter
Voltm eter and O hmm eter each have a
particular application for trouble shooting
electrical circuits.
When using a ammeter or voltmeter and the
value being tested is unknown always use the
highest scale first and work downward to a
midscale reading whenever possible. This will
avoid damage to the instrument.
Never use an ohmmeterr in a power circuit or
as a substitute for a voltmeter or ammeter as
damage to the instrument w ill result.
AMMETER (Figure 1 and 15)
Disconnect the circuit from the power source before
connecting the ammeter. The ammeter measures the
amount of electrical current, amperes, moving through a
conductor. The ammeter must be placed in series with the
circuit being tested. Be sure that the ammeter’s positive
terminal is connected to the positive (battery) side of the
circuit and is negative terminal to the negative (ground)
side of the circuit.
OHMMETER (Figure 13 and 15)
The ohmmeter is an instrument designed to indicate
resistance in ohms. It is used to test the condition of a unit
disconnected from the circuit.
Ohmmeter Calibration
When the ohmmeter probes are connected together, a
circuit is completed causing the meter needle to deflect.
The needle should read ZERO ohms, if it does not, rotate
the CAL or ADJ knob to ZERO the needle.
When the probes are held apart, the needle moves to
the maximum (infinite) resistance side of the scale.
The meter is now ready for use. Refer to figure 14 for a
typical application of the ohmmeter.
WIRING DIAGRAMS 10
VOLTMETER (Figures 14 and 15)
The voltmeter (properly observed) will give the
technician more information than the ammeter, ohmmeter
and test light combined. Its application for troubleshooting
here is to measure the electrical pressure (voltage) drop in
a resistance circuit (figure 14).
To use a voltmeter for troubleshooting an electrical
problem, connect it in parallel with the existing circuit
(figure 1 ). If the voltmeter is connected in series with the
circuit being tested, the nature of the circuit would be
changed and the reading would have no particular value
or use. Connect the meter terminals according to polarity
as shown in figure 14.
The dash mounted voltmeter (in the vehicle) should
also be observed for monitoring proper operation of the
generator battery cranking motor, and cranking circuit. In
this application, battery voltage drop can be monitored
while the engine is cranking; and after the engine is
running, generator output voltage can be monitored. This
can be a valuable first step prior to diagnosing other
electrical problems.
WIRING HARNESS AND WIRES
Every wire is a specific size with colored or striped
insulation that is indicated on the wiring diagrams.
Insulation colors help to trace circuits and to make proper
connections. Abbreviations and symbols used for
indicating wire insulation colors and patterns are as
follows:
................. Blue
BLK ........... ............. Black BLU
BRN ........... ........... Brown PPL.
CHK ........... ........... Check TR . .
C R ........... ............. Cross YEL .
GRN........... ............. Green II... .
NA T .........
........... Natural WHT
SG L ........................Single STR .
O R N ........
...........Orange PNK
G R ........... ............... Gray DK . .
. .Yellow
.Parallel
.Stripe
. .Pink
. .Dark
Some wires are grouped and taped together or
encased in a split plastic casing. This grouping of wires is
called a harness. For some purposes, it is more practical
to use a single wire protected by a braided tubing called a
loom.
VOLTS
VOLTMETER SCALE: Volts through 15 Volts
A = 3 Volts
B = 7 Volts
C = 13 Volts
AMPERES
AMMETER SCALE: Amperes through 1 Am peres
E = 1 Ampere
F = 1.8 Amperes
G = 9 Amperes
OHMMETER SCALE: 0 Ohms through Infinity ( o o )
H = 5 Ohms
I = 36 Ohms
J = 115 Ohms
K =35 Ohms
F- 1778
Figure 15—Meter Scales

WIRING DIAGRAMS 11
Wiring harnesses are joined by using a multiple plug
and receptacle connector block, or a terminal post
chassis junction block. In the instrument panel area
plastic insulated blade-type connectors and screw-type
terminals are used.
Each harness or wire must be held securely in place by
clips or other holding devices to prevent chafing of the
insulation.
WIRE SIZE
Wire size in a circuit is determined by the amount of
current, the length of the circuit and the voltage drop
allowed. Wire size is specified using the metric gage. The
metric gage describes the wire size directly in cross
section area measured in square millimeters.
WIRE SIZE
CONVERSION TABLE
METRIC
SIZE
(mm)
0.22
.35
.5
0.8
1.0
2.0
3.
5.
8.0
13.
19.
32.
4 .
5 .
62.
AWG
SIZE
24
20
18
16
14
12
10
8
6
4
2
1
00
ON-VEHICLE SERVICE
CIRCUIT MAINTENANCE
AND REPAIR
MAINTENANCE AND REPAIR
All electrical connections must be kept clean and tight.
Loose or corroded connections may cause a discharged
battery, difficult starting, dim lights, and possible damage
to the generator and regulator. Wires must be replaced if
insulation becomes burned, cracked, or deteriorated.
To splice a wire or repair one that is frayed or broken
always use rosin flux solder to bond the splice and
insulating tape to cover all splices or bare wires.
When replacing wire, it is important that the correct size
wire be used as shown on applicable wiring diagrams or
parts book. Each harness or wire must be held securely in
place to prevent chafing or damage to the insulation due
to vibration.
Never replace a wire with one of a smaller size or
replace a fusible link with a wire of a larger size.
WIRING CONNECTOR TERMINAL
REPLACEMENT (BLADE TYPE)
Remove or Disconnect (Figure 16)
1. Terminal lock tang.
2. Terminal (61).
Install or Connect (Figure 17)
1. Pry up on the tang (7 ).
2. Terminal into the connector.
Figure 16—Removing the Terminals from
the Connector
WIRING CONNECTOR TERMINAL
REPLACEMENT (TWIN LOCK TYPE)
Remove or Disconnect (Figure 18)
Tool Required:
J-22727 Terminal Remover
1. Connector lock tangs.
2. Terminal locks using J-22727.
3. Terminal.
Install or Connect
1. Pry out the tangs.
2. Terminal into the connector.
WIRING DIAGRAMS 1
With the low current and voltage levels found in some
circuits, it is important that the best possible bond at all
wire splices be made by soldering the splices.
Use care when probing the connections or replacing
terminals in them, it is possible to short between opposite
terminals. If tnis happens to the wrong terminal part, it is
possible t' at damage may be done to certain
com poner :. Always use jum per w ires between
connectors for circuit checking. Never probe through the
Weather-Pack seals.
When diagnosing for possible open circuits, it is often
difficult to locate them by sight because oxidation or
terminal misalignment are hidden by the connectors.
Merely wiggling a connector on a sensor or in the wiring
harness may correct the open circuit condition. This
should always be considered when an open circuit is
indicated while troubleshooting. Intermittent problems
may also be caused by oxidized or loose connections.
Figure 17—Resetting the Lock Tang
WEATHER-PACK CONNECTORS
Special connectors known as Weather-Pack connectors
(figure 19) require a special tool J-28742 for servicing.
This special tool is required to remove the pin and sleeve
terminals. If removal is attempted with an ordinary pick,
there is a good chance that the terminal will be bent or
deformed. Unlike standard blade-type terminals, these
terminals cannot be straightened once they are bent.
Make sure that the connectors are properly seated and
all of the sealing rings in place when connecting the
leads. The hinge-type flap provides a back-up, or
secondary locking feature for terminals. They are used to
improve the connector reliability by retaining the terminals
if the small terminal lock tangs are not positioned
properly.
Molded-on-connectors require complete replacement of
the connection. This means splicing a new connector
assembly into the harness. Environmental connections
cannot be replaced w ith standard connections.
Instructions are provided with the Weather-Pack
connector and terminal packages.
METRI-PACK CONNECTORS
The Metri-Pack connectors use a pull-to-seat type
terminal, as shown in figure 19. The special tool required
to remove the terminal is J-35689-A terminal remover. If
removal is attempted with an ordinary pick, there is a
good chance that the terminal will be bent or deformed.
Refer to figure 19.
Remove or Disconnect (Figure 19)
Tool Required:
J-28742 Terminal Remover
Primary lock (121) by lifting.
Connector sections.
Secondary lock (125) by spreading the sides of the
hasp, thus clearing the staples and rotating the
hasp (127).
Terminal (131) by using J-28742 (128).
• Snip off the old terminal assembly.
5 mm of the wire insulation (13 ).
Clean
Terminal barrel (124).
Install or Connect (Figure 19)
Terminal insulator (134) on the wire. Slide the
insulator back on the wire about 8 cm (3 inches).
Terminal (131) on the wire.
• Roll crimp (132) and solder the terminal.
Terminal insulator (134) and the roll crimp (133).
Terminal into the connector.
Secondary lock (125).
Connector sections until the primary lock (121)
engages.
4.
5.
EE
METRI-PACK CONNECTOR REPLACEMENT
Remove or Disconnect (Figure 19)
Tool Required
J-35689-A Terminal Remover
1. Primary lock (121) by lifting.
2. Connector body (137).
3. Connector seal (12 ) by pulling the seal back onto
the wires away from the connector body (137).

WIRING DIAGRAMS 13
12 ,121 122
---------- , /136
1 6
130
1 9
134
133
1 1 137 1 0
VIEW A
136
138 137 139
139
138
VIEW B
12 . Connector Seal 13 . 5 mm ( .2 inch)
121. Primary Lock 131. Terminal
122. Secondary Lock Staple 132. Roll Crimp
123. Secondary Lock 133. Roll Crimp
124. Terminal Barrel 134. Terminal Insulator
125. Secondary Lock 136. Metri-Pack Series 15 Female Terminal
126. Lock Opened 137. Connector Body
127. Lock Opened 138. Locking Tang
128. J-28742 Terminal Remover 139. J-35689 Terminal Remover
129. Wire
F- 2349
Figure 19—Weather-Pack and Metri-Pack Connectors
WIRING DIAGRAMS 14
90. Jacket
91. Twisted Wires
9 . Splice Clip
93. Crimp and Solder
94. Electrical Tape Wrap
95. Outer Electrical Tape Wrap. B- 623
B
Figure 0—Twisted Wire Repair
4. Terminal (136) by inserting J-35689 (139) into the
connector body (137) to depress the locking tang
(138), then push the wire and terminal through the
connector body (figure 2 ).
• Snip off the old terminal unless the terminal is to be
reused, reshape the locking tang.
5. 5 mm ( .2-inch) of the wire insulation (13 ).
Clean
• Terminal cavity of the connector body.
Install or Connect (Figure 19)
1. Terminal (136) on the wire.
• Crimp and solder the terminal.
2. Terminal (136) into the connector cavity by pulling
the wire on the seal side of the connector until the
locking tang (138) is fully seated.
3. Seal (12 ) by pressing the seal into the connector
body (137) until it is fully seated.
4. Connector until the primary lock (121) engages.
WIRING REPAIR
The wire repair is very important for the continued
reliable operation of the vehicle. This repair must be done
as described in the following procedures.
Twisted Wires (Figure 0)
«■+ Remove or Disconnect
101 10 103
V \
106
V
107
1 . Jacket
1 1. Aluminum/Mylar Tape
1 2. Drain Wire
1 3. Splice Clip
1 4. Crimp and Solder
1 5. Electrical Tape Wrap
1 6. Drain Wire Splice Clip, Crimped And Sol
dered.
1 7. Outer Electrical Tape Wrap.
B- 6231
Figure 1—Twisted/Shielded Wire Repair
3. Insulation from the wire.
Install or Connect
1. Splice clip (93).
• Crimp.
• Solder.
2. Electrical tape wrap (94) on wires.
3. Outer electrical tape wrap (95).
Twisted Wires/Shielded Cable (Figure 1)
Remove or Disconnect
1. Jacket (1 ).
2. Unwrap aluminum/mylar tape (1 1).
3. Drain wire (1 2).
4. Leads.
5. Insulation on the leads.
+«- Install or Connect
1. Jacket (9 ).
2. Twisted wires (91).
1. Splice clips (1 3).
2. Crimp and solder the splice clips (1 4).
3. Electrical tape (1 5) on the splices.

WIRING DIAGRAMS 15
4. Aluminum/mylar tape by wrapping and taping.
5. Drain wire with a splice clip (1 6). Crimp and solder
the splice clip.
6. Outer jacket electrical tape wrap (1 7).
SPECIAL TOOLS

1988 C/K TRUCK
SECTION A
PAGE DESCRIPTION PAGE DESCRIPTION
POWER DISTRIBUTION (GASOLINE) 34 ELECTRONIC CONTROL MODULE (ECM)-OUTPUTS (DIESEL)
3POWER DISTRIBUTION (DIESEL) 36 ECM CHART (DIESEL)
4 AUXILIARY BATTERY(RPO TP ) 38 AUTO TRANSMISSION KICKDOWN SOLENOID (M40)
5 FUSE BLOCK 39 HEATER
6CONVENIENCE CENTER 40 AIR CONDITIONING
7HEADLAMPS & PARKING LAMPS (BASE) 4 BRAKE WARNING SYSTEM
8 HEADLAMPS & PARKING LAMPS (QUAD) 43 INSTRUMENT PANEL LAMPS (ELECTRONIC)
9 MARKER LAMPS (QUAD ONLY) 44 INDICATOR LAMPS (ELECTRONIC)
11 ROOF MARKER LAMPS 46 SEAT BELT WARNING BUZZER
1 HAZARD LAMPS 47 FOUR WHEEL DRIVE INDICATOR
14 DIRECTIONAL LAMPS 48 DOME LAMPS
16 HORNS 49 CONVENIENCE LIGHTING PACKAGE
17 START 50 CARGO LAMP
18 START (DIESEL) 51 RADIO EQUIPMENT
19 IGNITION 5 RADIO EQUIPMENT
0 THROTTLE BODY INJECTION 53 POWER WINDOWS
1 HOT FUEL HANDLING 54 REAR DEFOGGER
GLOW PLUGS (DIESEL) 55 POWER DOOR LOCKS
4 ENGINES CONTROLS (DIESEL) 56 WIPER/WASHER
6 FUEL CONTROL & IDLE AIR CONTROL 57 CRUISE CONTROL
7 AUXILIARY COOLING FAN 58 REAR WHEEL ANTI-LOCK
9 ELECTRONIC CONTROL MODULE (ECM)-INPUTS 59 BACK-UP LAMPS
30 ELECTRONIC CONTROL MODULE (ECM)-OUTPUTS 61 END GATE & SIDE CLEARANCE LAMPS
3 ECM CHART 6 TAIL LAMPS
33 ELECTRONIC CONTROL MODULE (ECM)-INPUTS (DIESEL) 64 LICENSE LAMPS
INDEX
SECTION A-PAGE 1

d-
o-
o
ao-
03; O r
9i
°o;
e>r a;
i SPLICE
2
^ A‘ W <■ »■-'
V :—M
-------- w—
'—X » — V
j-I
<
15 -32 BLK
15 -8. BLK
SHEET
METAL
GRD REAR
POWER DISTRIBUTION
LB4, L03, L05, L19
SECTION A-PAGE
AUXILIARY
BATTERY
RPO-TP2
(IF EQUIPPED)
SHEET
METAL
GROUND
FUSE BLOCK

__ n ____ n __
+ “SHEET
—n -------- n—
+ -
RH METAL LH
BATTERY GRD BATTERY
FRONT REAR
FUSE BLOCK POWER DISTRIBUTION
LH6, LL4 DIESEL
SECTION A-PAGE 3

JUNCTION
BLOCK
AUXILIARY
BATTERY
RELAY
A
O
O
o
o
o
V
© J O - 2-3. RUST
‘ FUSIBLE LINK '
SPLICE
2
2-3. RUST
FUSIBLE LINK '
SPLICE
2
15 -3. BLK-
GROUND
5 )
D
Ui
C
*
AUXILIARY
BATTERY
-2 -8. RED-
© S 3 -2 -8. BLK/RED-
IT
teDOOCgDOO Cgp
G C i D
-5 -2. BRN-
1T
I J *_J
tCM tGtt 1**
M f EDO
GCi O O DC 0 0 m s
Q Q O O O O O O o o
»T 0f HA I CM M
II II II II II" II II II LL "
□ □ a/is □ □
□ □ ffl/B □ □
H /E □ □ f i l /l l E /E
e/e □ □ e/ts □ □
E /E □ □ E / E □ □
FRONT
FUSE BLOCK
FROM PANEL
DIMMER
SWITCH
FROM LH
JAMB SW
FROM
HEATER A/C
■ 15 -3. BLK
GROUND FROM RADIO
FROM CIGAR
LIGHTER
FROM SEAT
BELT SW
REAR
TO HEATER A/C
SPLICE
5
15 -3. BLK-
a n a s
•west »<wa Mr m c*unt
iT flE fu frO
2*S| EW BS-
M MfOQ tfAM I— Mt* MfOO -I *»• ANT C*M0 L*
jj n* * c SffitWii •* t e
A A A A A
FROM
CONVENIENCE
CENTER
WOO 4WMII10I
Q Q3°(H3 Q
a C3GD 3 CD a
——
12 59236
On
12 59229
CONVENIENCE
CENTER l “L r 12 33713
GROMMET
12 591 5
-5 .8 BRN-
62887 4
ID ■15 - 8 BLK-
■ 5 -.8 BRN -
■ 15 *.8 BLK -
2
CL
CO
1
o
62887 4
AUXILIARY BATTERY RPO TP
SECTION A-PAGE 4

50- .0 BRN-HEATER-AIR CONDITIONING
FRONT
40 .8 ORN/WHT-INTERIOR LPS
40 .8 ORN LT SWITCH-CONV CENTER
4-3.0 BRN-IGN SW-ACC
93-1.0 WHT-W /S WASHER WIPER
43 .8 YEL-RADIO
76-3.0 PNK —POWER WINDOWS
4-3.0 BRN-IGN SW-ACC
60 .8 ORN/WHT-POWER/ACC
-3.0 RED-IGN SW-BATT
806 .8 PPL/WHT-CRANK
6-3.0 PPL-STARTER SOLENOID FEED
8 .35 GRA-PANEL LAMPS
-3.0 RED-IGN SW-BATT
300-3.0 ORN —IGNITION
50 .8 BRN/WHT-REAR WHEEL
ANTILOCK
39 .8 PNK/BLK—IGN SPLICE
3-3.0 PNK—IGN SW-IGN
SHUNT (TYP.)
38-1.0 DK BLU-DIR SIGN FLASHER
75 .8 DK BLU-BACKUP LAMP SW
439 .8 PNK/WHT—ECM/IGNITION
3-3.0 PNK —IGN SW -IGN
481-.8 RED-INJECTOR
!N I
"A ^ J
GAS
ENGINES
ONLY
44 .8 DK GRN-LT SW RHEOSTAT
-3.0 RED-BATTERY
140-.8 ORN-HAZARD FLASHER
REAR
FUSES AMP COLOR
1 004005 5 TAN
1 004007 10 RED
1 004008 15 LT BLU
1 004009 0 YEL
1 004010 5 WHT
FUSE BLOCK
SECTION A-PAGE 5

----- CRUISE CONTROL
TURN
SIGNAL
FLASHER
POWER
DOOR LOCKS
REAR
DEFOGGER
HORN RELAY
POWER
WINDOWS
FOUR
WHEEL-
DRIVE
ROOF
MARKER-
LAMPS
DOME LAMP
REAR
DEFOGGER
CARGO LAMP
POWER
WINDOWS
INTERIOR
COURTESY
LAMPS
AUXILIARY
BATTERY
RELAY
INTERIOR
COURTESY
LAMPS
POWER
DOOR
LOCKS
1 059 9 AUDIO ALARM MODULE
FRONT
CONVENIENCE CENTER
SECTION A-PAGE 6
8 .5 GRA
39 .8 PNK/BLK
437 .8 BRN
450-.8 BLK/WHT
40 .8 ORN
156.8 WHT
156.8 WHT
150.8 BLK
9 .8 BRN
150-3.0 BLK-
37 .8 YEL-
150-.8 BLK-
38 .8 BLK-
8 .35 GRA-
140 .8 ORN-
80-.8 LT GRN-
S f f l Gp □
39- 8 PNK/BLK-
150 .8 BLK
60-3.0 ORN/BLK
38-1.0 DK BLU
38-1.0 DK BLU
150-1.0 BLK
16 .8 PPL
40-.8 ORN
40-1.0 ORN/BLK
40-.8 ORN/BLK
8- 5 BLK
9-1.0 DK GRN
76-3.0 PNK
50- .0 BRN
9 .8 BRN
1 50-.8 BLK
REAR

GROUND FROM ENGINE
COOLANT FAN
(L19 ONLY
RIGHT HAND
HIGH & LOW
BEAM
HEADLAMPS
LEFT HAND
HIGH & LOW
BEAM I Z
HEADLAMP
FROM
WINDSHIELD
WASHER PUMP HEAD LAMPS & PARKING LAMPS (BASE)
SECTION A-PAGE 7

TO
RIGHT HAND
PARK &
TURN SIGNAL
LAMPS
TO
LEFT HAND
PARK &
TURN SIGNAL
LAMPS
RH
SIDE
MARKER
LAMP
Z
a: a.
m cd
oo CO
2
cc
CO
A O) >
O iJ
SPLICE 9
JUNCTION
BLOCK DIESEL
6294 15
LH
SIDE
MARKER
LAMP
MARKER LAMPS (QUAD ONLY)
SECTION A-PAGE 9

V
SECTION A-PAGE 10