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Battery System Operation
Ether Starting System Operation

TM-9-2320-272-24-1 Truck 5-Ton 6x6 M939 M939A1 M939A2 Series Trucks (Diesel) Manual
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TM 9-2320-272-24-1
1-22. ELECTRICAL SYSTEMS OPERATION (Contd)
b. Starting System Operation.
The starting system is identical for all models covered in this manual and consists of the following major
components and circuitry:
Key Item and Function
8  BATTERY SWITCH - Completes circuit 459, closing a relay in the protective control box to supply
power to ignition switch through circuits 5 and 5B.
9  PROTECTIVE CONTROL BOX - Locks out starter circuit, which prevents starter from reengaging
while engine is running.
1 0  IGNITION SWITCH - Provides battery power to fuel solenoid through circuit 54 and the neutral
start safety switch through circuit 498.
11  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.
12  STARTER SOLENOID - A magnetic relay that is powered by circuit 74 to transmit 24-volt battery
power to the starter motor through circuit 6.
13  STARTER MOTOR - Cranks engine for starting. Supplied with 24-volt battery power through
circuit 6.
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