Alternator Tests

Remove individual connectors from alternator. Turn ignition switch to "ON" position. Connect negative voltmeter lead to ground. Attach positive lead, in turn, to each disconnected lead. Voltmeter should indicate battery voltage at each lead.
If reading is zero (0) at main output lead, check wiring to starter solenoid and battery. If zero (0) when connected to "IND" lead, check for ground or open circuit between warning light and alternator connector.
If reading is zero (0) when connected to "S" lead, check wiring back to starter solenoid and battery. A break in the sensing lead will result in alternator not charging and warning light not working.
Attach connectors to alternator. Turn ignition switch to "ON" position. With negative lead of voltmeter still attached to ground, connect positive lead to "IND" terminal. See Fig 1. Voltmeter should indicate approximately 2 volts.

Fig 1: Test Voltage at "IND" Terminal Alternator connectors should be in place.
If reading is zero (0), suspect surge protection diode. If voltmeter indicates battery voltage, suspect brushes, rotor, or regulator.
With voltmeter negative lead attached to ground, attach positive lead to metal link on regulator. See Fig 2. Turn ignition switch to "ON" position. Voltmeter should indicate approximately 0.5 volt. If 12 volts are indicated, regulator is faulty.

Fig 2: Test Voltage at Regulator Metal Link If 12 volts are indicated, regulator is faulty.
If reading is now 0.5 volts, but 12 volts was registered in step 5), check brushes, rotor, and slip rings.
NOTE: If warning light operates with ignition in "OFF" position, but goes out when switch is in "ON" position, check voltage at "IND" terminal with switch in "OFF" position. If battery voltage is indicated, diode pack is faulty.
Start engine, and run it at a constant 2500 RPM. With voltmeter negative lead attached to ground, attach positive lead to "IND" terminal. See Fig 3. Note voltage. Connect positive lead to alternator's main output terminal. Voltage readings should be the same. If a difference of more than 0.5 volt exists, suspect diodes.

Fig 3: Test Voltage at "IND" and Main Output Terminals Readings should be same with engine at 2500 RPM.
Connect voltmeter between battery insulated terminal and alternator's main output terminal. See Fig 4. Start and run engine at approximately 2500 RPM. Voltmeter should not exceed 0.5 volt.
If higher reading exists, check wiring from alternator to battery for loose or dirty connections.
NOTE: If warning light glows while engine is running at normal charging speeds, problem may be a faulty diode pack or dirty or loose connections in battery-to-alternator wiring.

Fig 4: Test Voltage at Main Output and Battery Insulated Terminals If more than 0.5 volt, check battery-to-alternator circuit.
Disconnect battery ground cable. Disconnect alternator. Connect ammeter between main terminal and disconnected main lead. See Fig 5. Connect a jumper wire between "IND" terminal and "IND" lead.

Fig 5: Test Voltage Under Accessory Load Ammeter should indicate maximum alternator output.
Reconnect battery cable, and switch on all accessories (except wipers) for 1 minute. Start and run engine at normal charging speed. Ammeter would indicate maximum output for alternator.
If output is low, use jumper wire to short metal link on regulator to ground, and repeat step 12). If maximum output is now indicated, suspect regulator. If output is still low, suspect stator windings.
Disconnect battery ground cable. Connect ammeter in series with alternator main output cable and starter solenoid. Reconnect battery cable. Connect voltmeter across battery terminals.
Start and run engine at 1500 RPM, until ammeter reads less than 10 amps. Voltmeter should read 13.6-14.4 volts. An incorrect reading indicates faulty regulator.