Alternator Troubleshooting

The alternator warning lamp should light as soon as the ignition is switched on, and the lamp should go out soon after the engine starts. However, if there is a fault in the charging system the warning lamp should remain on while the engine is running.
1. If indicator does not light momentarily when ignition switch is turned on:
a. Check that voltage regulator electrical connector is properly seated.
b. Check alternator ground. Resistance between alternator frame and negative battery post should be less than 2 ohms.
c. Check that bulb is not blown by grounding .25 in. ``L'' terminal on connector. Bulb should illuminate.
2. If indicator comes on while engine is running:
a. Check alternator belt for breakage or incorrect tension.
b. Check for broken charging lead.
c. Check for internal damage to alternator.
d. Check for malfunctioning regulator.
3. If charging voltage is consistently below 13.5 volts but the indicator functions normally, check the following:
a. Defective diodes. Diode should have continuity with current applied in one direction and no continuity with current applied in opposite direction.
b. Open stator windings.
c. Excessive carbon on slip rings.
d. Worn or sticking brushes.
e. Poor electrical connections.
f. Defective battery.