TM-9-2320-283-20-1
TRUCK TRACTOR, LINE HAUL, 50,000 GVWR, 6X4, M915A1
TECHNICAL MANUAL; ORGANIZATIONAL MAINTENANCE PART 1 OF 3
DECEMBER 1983
TM-9-2320-283-20-1 - Page 64 of 926
TM 9-2320-283-20-1
PRINCIPLES OF OPERATION.
1-15.
ELECTRICAL SYSTEM (Continued).
c.
Service Lighting System (Continued).
(5)
Instruments, Gages, Dome Lamp, and Map Lamps.
Instrument gages operate when ignition switch is in ON position.
Instrument lamps illuminate when headlamp switch is
pulled to ON position.
Dome lamp and map lamps illuminate whenever dome or map lamp switches are on and blackout
toggle switch is in NORMAL position.
BATTERY PACK.
Consists of four, 12-volt, maintenance free batteries.
Two batteries
are wired in parallel in each set.
Each set is connected in series
for 24-volt
output.
Battery pack
is used
for both 12-volt and 24-volt output.
IGNITION SWITCH.
Supplies 24-volt power to relay (RY-9), which in turn provides 12-volt power to electrical system,
including instrument gage,
dome lamp, and map lamp circuits.
RELAY
(RY-9).
Energized by 24-volt power from ignition switch.
When energized, RY-9 supplies 12-volt power to circuit
breaker (CB-2).
CIRCUIT BREAKER (CB-2).
Protects electrical components of instrument gage circuit by opening when load exceeds 20
amperes.
May be manually reset by pressing CB-2 button in.
WATER TEMPERATURE GAGE.
Changes in water temperature cause sending unit to increase and decrease
resistence
in
circuit.
As resistence changes, voltage at gage is changed, operating gage.
FUEL LEVEL GAGE.
Changes in fuel level cause sending unit to increase and decrease resistence in circuit, as
resistence changes, voltage at gage is changed, operating gage.
VOLTMETER.
In series with 12-volt system.
Shows voltage in system when ignition switch is in either ACCESSORY or
IGNITION (ON) position.
TRANSMISSION OIL TEMPERATURE
GAGE.
Changes in transmission temperature cause sending unit to increase
and decrease resistence in circuit.
As resistence changes, voltage at gage is changed, operating gage.
ENGINE OIL PRESSURE GAGE.
Changes in engine oil pressure cause sending unit to increase and decrease resistence
in circuit as resistence changes, voltage at gage is changed, operating gage.
CIRCUIT BREAKER
(CB-5).
Protects 12-volt electric horn and turn signal flasher circuits.
1-44
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