Description; Speedometer; Fuel Gage; Oil Pressure Gage - GMC G Service Manual

8C-2 INSTRUMENT PANEL

SPEEDOMETER

The speedometer on the instrument panel is a mechani­
cal type that is driven by a cased cable which is connected
to the transmission. The speedometer is located in the cen­
ter of the instrument panel. Refer to "Diagnosis of the
Speedometer System" for diagnosis.

FUEL GAGE

The fuel gage is an electrical, current sensing type of
indicator. It has two coils in it. One coil sets up a constant
magnetic field. The other coil has a varying magnetic field
which is varied by the rheostat attached to a float in the fuel
tank. A magnet, attached to a pointer, is located between
the two coils. The magnet will establish a position which is
controlled by the magnetic fields of the two coils. Refer to
figure 1 for diagnosis.

OIL PRESSURE GAGE

The oil pressure gage displays the engine oil pressure.
The gage is electrical. The sender is a variable resistance
which controls the current passing through the gage. Refer
to figure 2 for diagnosis.

TEMPERATURE GAGE

This gage displays the temperature of the engine cool­
ant. It is an electrical gage. The gage's sender is a variable
resistance that controls the current passing through the
gage. Refer to figure 3 for diagnosis.

DESCRIPTION

ENGINE CONTROL/IGNITION
On the R/V and G-models, the engine control/ignition
switch is located in the steering column on the right side just
below the steering wheel. The electrical switching portion of
the assembly .is separate from the key and lock cylinder.
However, both are synchronized and work in conjunction
with each other through the action of the actuator rod
assembly.
For a complete explanation of the key and lock cylinder,
and the actuator rod assembly, refer to STEERING COL­
UMN, (SEC. 3B4).
The ignition and starting switch (gasoline engine) is key
operated through the actuator rod assembly to close the
ignition primary circuit and to energize the starting motor
solenoid for cranking.
The engine control switch (diesel engine) actuates the
glow plugs and glow plug relay assembly when the switch is
turned to the run position. A "GLOW PLUGS" lamp on the
instrument panel remains lit until the glow plugs have pre­
heated the combustion chamber. Turning the engine con­
trol switch to the start position after the "GLOW PLUGS"
lamp turns off engages the starter motor solenoid for
cranking.
On the P-models the engine control/ignition switch is
located on the instrument panel. The switch controls the
engine run and start functions, and the accessories.
The connections to the engine control/ignition switch are
shown in the Wiring Diagrams Booklet. The charts included
on the diagrams show how the switches are internally con­
nected in each switch position.
The lamp switch controls the headlamps, marker lamps,
running lamps and parking lamps. The switch also controls
the dome lamps and the light level of the instrument illumi­
nation lamps.
SWITCH

LAMP SWITCH