Current Output Test
- Turn ignition switch to OFF position. Disconnect negative battery cable. Disconnect alternator output wire from terminal "B". See Fig 1. Using an ammeter, connect positive ammeter lead to terminal "B" and negative lead to disconnected alternator output wire.
- Using a voltmeter, connect positive voltmeter lead to alternator terminal "B" and negative lead to ground. Install tachometer. Connect negative battery cable. Start engine. Turn headlights on high beam and heater switch on HIGH. Increase engine speed to 2000 RPM and note maximum current output on ammeter.
- If maximum current output is within 10 amps of rated amp output (55 amps) and voltmeter reading is 13.5-16.0 volts, alternator is okay. If maximum current output is not within 10 amps of rated amp output and voltmeter reading is less than 13.5 volts, repair or replace alternator.
Courtesy of GENERAL MOTORS CORP.