Troubleshooting: Delco CS130 and CS121 Rebuild Instructions, Part 3

A basic wiring diagram is shown in Figures 3 and 3A. When operating normally, the indicator bulb will come on when the switch is turned on, and will then go out when the engine starts. If the indicator operates abnormally, or if an under-charged or overcharged battery condition occurs, the following procedure may be used to diagnose the charging system. Remember that an undercharged battery is often caused by accessories being left on over-night, or by a defective switch which allows a bulb, such as a trunk or glove box light, to stay on. This alternator does not have a regulator by-pass test hole.
Observe the following procedure:

1. Visually check belt and wiring and load check battery .
2. Go to step V. for vehicles without charge indicator light.
3. With ignition switch on and engine stopped, light should be on. If not, detach harness at alternator, use fused jumper to ground "L" terminal lead on harness. Be very carefully to properly identify "L" terminal lead. Grounding "L" terminal should cause indicator light to light. If lamp does not light, locate open circuit between grounding lead and ignition switch. Bulb may be bad.
4. Switch on, engine running at moderate speed. Light should be off. If not, stop engine, turn switch on, and detach wiring harness at alternator.
1. If light goes off, replace or repair alternator.
2. If light stays on, check for grounded "L" terminal wire in harness.
5. Battery undercharged or over-charged.
1. Detach wiring harness connector from alternator.
2. With switch on, engine not running, connect voltmeter from ground to "L" terminal in wiring harness, and to "I" terminal, if used. Wiring harness may connect to either "L" or "I" or both.
3. Zero reading indicates open or grounded circuit between terminal and battery. Correct as required.
4. Re-connect harness connector to alternator, run engine at moderate speed with all electrical accessories turned off.
5. Measure voltage across battery. If above 16.0, replace or repair alternator. NOTICE: The alternator may be O.K. on vehicles using "S" terminal if "S" terminal wiring has excessive resistance which will cause high voltage. Refer to vehicle wiring diagram. Correct wiring as needed, then re-check voltage.
6. Connect ammeter at alternator output terminal. Connect voltmeter across alternator. Turn on accessories. load battery with carbon pile to obtain maximum amperes output. Maintain voltage at 13.0 or above.
1. If within 15 amperes of rated output, alternator is O.K.
2. If not within 15 amperes of rated output. Check belt for slippage or replace or repair alternator.