CHARGING SYSTEM TROUBLESHOOTING

TM 10-3930-638-24&P

2-22. CHARGING SYSTEM TROUBLESHOOTING (cont)

MALFUNCTION

TEST OR INSPECTION

CORRECTIVE ACTION

1. ABNORMAL ALTERNATOR LIGHT OPERATION (cont)

STEP 1. (cont)

b. If ALTERNATOR light is on, grasp and pull

connector from alternator terminals 1 and 2.

If the ALTERNATOR light goes out, replace

the alternator (para 2-26).

If the light stays on, check for a short between

these wires, then install connector on

alternator terminals 1 and 2.

Step 2. Place IGNITION switch to ON with engine stopped. ALTERNATOR light should be on.

With engine running, ALTERNATOR light should be off.

a. If ALTERNATOR light is off with engine stopped, or on with engine running, check for an open

circuit between alternator terminal l and ALTERNATOR light. Use an ohmmeter to check

diode and 40 ohm resistor in ALTERNATOR light circuit.

b. If circuit tests are satisfactory, troubleshoot alternator (MALFUNCTION 2 below).

2. ALTERNATOR OUTPUT LOW, UNSTEADY OR ZERO

Turn IGNITION switch to ON and alternately connect voltmeter leads from ground to alternator

Step 1.

terminal 1, terminal 2 and B terminal.

a. If voltmeter indicates 24 Vdc at

all three terminals, proceed to

step 2.

b. If voltmeter does not indicate

24 Vdc at one or more terminals,

check for an open circuit

between battery positive post

and affected alternator

terminal.

Step 2. Disconnect battery ground cable and

connect an ammeter between

alternator B terminal and starter

relay terminal 3.

Reconnect battery ground cable, and

connect a carbon pile across batteries.

Turn all vehicle lights on to increase

load on batteries, and operate engine

at 1800 rpm.

a. If ammeter indicates 27 to 47 amperes, but ALTERNATOR light stays on, check for open

circuit from alternator terminal 1 in wiring, diode, and 40 ohm resistor.

b. If ammeter does not indicate 27 to 47 amperes, replace alternator (para 2-26).