Symptom Related Diagnostic Procedures

Does Not Illuminate w/Ignition On (Engine Not Started)

Possible open circuit between alternator D + and indicator light.
1. Remove alternator cover, then disconnect D + wire from alternator.
2. Connect a jumper wire between D + and ground, then turn ignition switch to On position.
3. If indicator light illuminates, proceed as follows:
a. Check for improper alternator ground, worn carbon brushes, defective voltage regulator or rotor.
b. If alternator grounding and brushes are defective, make necessary corrections. If light now illuminates, system is operating properly.
c. If alternator grounding and brushes are satisfactory, replace voltage regulator. If light still fails to illuminate, replace alternator.
4. If indicator light does not illuminate, proceed as follows:
a. Indicator bulb is burned out.
b. Disconnect battery ground cable, replace bulb, reconnect ground cable and turn ignition switch to On position.
c. If indicator light illuminates, system is operating properly.
d. If indicator light does not illuminate, wiring between alternator D + and indicator light is open, repair as necessary.


Light Illuminated w/Ignition Off

Alternator diode(s) defective (rectifier bridge), replace alternator.


Light Does Not Go Out When RPM Increases

Check for slipping fan belt, short to ground between alternator D + and indicator light or alternator is defective, replace.

Possible Short To Ground Between Alternator D+ & Indicator Light

1. Disconnect alternator wiring, then turn ignition switch to On position.
2. If indicator light illuminates, there is a short to ground between alternator D + and indicator light. Repair as necessary.
3. If indicator light does not illuminate, test alternator output and voltage regulator. Replace defective component.