TM-9-2320-272-23-1
TRUCK, 5-TON, 6X6, M939, M939A1, AND M939A2 SERIES TRUCKS (DIESEL)
TECHNICAL MANUAL; FIELD MAINTENANCE MANUAL; VOLUME 1 OF 5
SEPTEMBER 2012
TM-9-2320-272-23-1 - Page 237 of 1313
INDICATOR, GAUGE, AND WARNING SYSTEM OPERATION
The indicator, gauge, and warning system is comprised of several subsystems:
A. ENGINE OIL PRESSURE INDICATOR
- Indicates engine oil pressure and receives battery power
through circuit 27A. Circuit 36 completes the circuit to ground through the oil pressure transmitter located
on the engine block.
B. FUEL INDICATOR
- Indicates fuel level. Receives battery power through circuit 27A. Circuit 28 or 29,
depending on which position fuel selector switch is in, completes the circuit to ground through the oil pressure
transmitter located on the engine block.
C. TRANSMISSION OIL TEMPERATURE INDICATOR
- Indicates transmission oil temperature and
receives battery power through circuit 27A. Circuit 324 completes circuit to ground through a temperature
sensor located in transmission.
D. FRONT-WHEEL DRIVE ENGAGEMENT LIGHT
- Informs the operator that front-wheel drive is engaged.
The system consists of a normally open pressure switch, which is powered through circuit 27A and an
indicator lamp powered through circuit 27A.
E. HORN SYSTEM
- The horn system consists of an air-operated horn that is controlled by an electric
solenoid. The solenoid is powered through circuit 26 and controlled by the horn switch through circuit 25.
F. SPRING BRAKE WARNING SYSTEM
- Warns the operator that spring brakes are applied. The system
consists of normally open pressure switch powered through circuit 37 and an indicator lamp which is powered
through circuit 37.
G. FAILSAFE WARNING SYSTEM
- Intended to give the operator an audible as well as visual signal of a
malfunction in one of the primary systems. Power for the system is supplied from the ignition switch through
circuit 564. The failsafe module causes an indicator lamp to illuminate and an alarm to sound when air
pressure falls below 60 psi (414 kPa) or when parking brake is set.
H. VOLTMETER
- Indicates system voltage and is connected to batteries through circuit 27A and to chassis
ground through instrument panel.
I. ENGINE COOLANT TEMPERATURE INDICATOR
- Indicates engine coolant temperature and receives
battery power through circuit 27A. Circuit 33 completes the circuit to ground through a coolant temperature
sensor that reacts to changes in engine coolant temperature by increasing or decreasing the resistance in
ground circuit.
TM 9-2320-272-23-1
0003
0003-32
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