TM 9-2320-272-24-1
1-22. ELECTRICAL SYSTEMS OPERATION (Contd)
Key Item and Function
chassis ground through instrument panel.
2 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.
3 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.
4 FUEL INDICATOR - Indicates fuel level. Receives battery power through circuit 27A. Circuit 28 or
29, depending upon which position fuel selector switch is in, completes the circuit to ground through
fuel level sensor.
5 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.
6 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.
7 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.
8 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.
9 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.
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