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 231 of 1313
STARTING SYSTEM OPERATION
The starting system is identical for all models covered in this manual and consists of the following major components
and circuitry:
A. PROTECTIVE CONTROL BOX
- Locks out starter circuit, which prevents starter from reengaging while
engine is running.
B. IGNITION SWITCH
- Provides battery power to fuel solenoid through circuits 54 and the neutral start
safety switch through circuit 498.
C. NEUTRAL START SAFETY SWITCH
- Prevents starter from energizing when vehicle is not in neutral,
by deenergizing circuit 499 and a relay in the protective control box, which disconnects power from circuit
74 and the starter solenoid.
D. STARTER SOLENOID
- A magnetic relay that is powered by circuit 74 to transmit 24-volt battery power
to the starter motor through circuit 6.
E. STARTER MOTOR
- Cranks engine for starting. Supplied with 24-volt battery power through circuit 6.
F. BATTERY SWITCH
- Completes circuit 459, closing a relay in the protective control box to supply power
to ignition switch through circuits 5 and 5B.
C
B
A
F
94
E
D
74
6
569
459
5
5B
54
499
498
G0030DAA
FUEL SHUTOFF SOLENOID
ON FUEL PUMP
BATTERY
Figure 18.
Starting System Components.
TM 9-2320-272-23-1
0003
0003-26
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