GMC ST 350 1988, Wiring Diagram

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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............................................................................................................................................................. 2
Tracing Circuits.................................................................................................................................................. 2
Basic Electric Circuits......................................................................................................................................... 2
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................................................................................................................................... 12
Metri-Pack Connectors.........................................................................................................................................12
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 2
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
G R N ................ Green
N A T .............. Natural
S G L ................Single
O R N .............. Orange
GR......................Gray
INSULATION
P P L ................Purple
TR....................Tracer
Y E L ................Yellow
I I ....................Parallel
W H T ................White
BLU....................Blue
STR.................. Stripe
PNK....................Pink
DK......................Dark
F-05975
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 150
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 19.0 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
sh ow s th e b a tte ry fe e d c o m in g fro m the P ow er
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.
C ircu it #6 goes through the clutch sw itch w ith 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.