Lighting System Troubleshooting.

Maintenance of the M939 Series Vehicles
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53

MULTIMETER CONNECTION TO

ALTERNATOR CIRCUIT 5.

Since battery voltage was not indicated, SSG Heatherly sets the

multimeter to an RX1 setting to read continuity. He then disconnects

the negative battery terminal and connects the positive meter lead to

circuit 568 wire and the negative meter lead to the circuit 5

alternator terminal.

At this point, the meter should indicate

continuity.

Since continuity is not indicated, this indicates that

there is an OPEN circuit.

He repairs circuit 568 as per the

instructions in paragraph 4-49 of TM 9-2320-272-20-1.

Lighting System Troubleshooting. In the following paragraphs we

will follow SGT Yowell as he troubleshoots the lighting system for

the malfunction HEADLAMPS (BOTH SIDES) INOPERATIVE and reaches the

conclusion that the headlamp beam selector switch is defective and

needs to be replaced.

The first thing that SGT Yowell does is read DA Form 2404 and

talk with the operator.

Once he has a better understanding of

the malfunction, he reads through the troubleshooting procedures to

determine the tools and special equipment necessary for this

task.

For this particular troubleshooting procedure, SGT Yowell

will

need

mechanic's

general

toolbox

and

multimeter.

Once

the

necessary

tools

and

equipment

have

been

gathered