TM-9-2320-272-24-1
TRUCK, 5-TON, 6X6, M939, M939A1, AND M939A2 SERIES TRUCKS (DIESEL)
TECHNICAL MANUAL; UNIT, DIRECT SUPPORT, AND GENERAL SUPPORT MAINTENANCE MANUAL; VOLUME 1 OF 4
JUNE 1998
TM-9-2320-272-24-1 - Page 59 of 1015
TM 9-2320-272-24-1
1-22. ELECTRICAL SYSTEMS OPERATION (Contd)
d. Generating System Operation.
The generating system is identical for all vehicles covered in this manual and consists of the following
major components and circuitry:
Key Item and Function
6
VOLTMETER
- Indicates electrical system voltage. It is connected to the electrical system through
circuit 27.
7
ALTERNATOR
- Rated at 26-30 volts, 60 amperes, the alternator assists and recharges batteries
during operation. A l00-ampere model is available as a kit.
8
CIRCUIT 3
- Provides a ground circuit to alternator.
9
CIRCUIT 566
- Controls a relay in protective control box that prevents starter from reactivating
while engine is running.
10
CIRCUIT 568
- Senses system voltage and excites the alternator field.
11
PROTECTIVE CONTROL BOX
- Connects circuit 5 to 81 to power the electrical system and
charge the batteries.
12
CIRCUIT 5
- Conducts alternator output to charge batteries and maintain vehicle voltage.
13
BATTERY SWITCH
- Closes relay in protective control box that connects battery circuits.
1-49
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