Alternator Tests

Remove individual connectors from alternator. Turn ignition switch "ON". Connect negative voltmeter lead to ground. Attach positive lead, in turn, to each disconnected lead. See Fig 1. Voltmeter should indicate battery voltage at each.
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 "ON". With negative lead of voltmeter still attached to ground, connect positive lead to "IND" terminal. See Fig 2. Voltmeter should indicate approximately 2 volts.

Fig 1: Voltage Test with Alternator Connectors Removed
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Connect voltmeter positive lead, in turn, to each wire .
If reading is zero (0), suspect surge protection diode. If voltmeter indicates battery voltage, suspect brushes, rotor or regulator.

Fig 2: Voltage Test at "IND" Terminal
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Alternator connectors should be in place .
With voltmeter negative lead attached to ground, attach positive lead to metal link on regulator. See Fig 3. Turn ignition switch "ON". Voltmeter should indicate approximately 0.5 volt. If 12 volts is indicated, regulator is faulty.

Fig 3: Voltage Test at Regulator Metal Link
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If 12 volts is 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 "OFF", but goes out when switch is "ON", 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 4. Note voltage. Then 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 diode pack.

Fig 4: Voltage Tests at "IND" and Main Output Terminals
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Run engine at 2500 RPM. Readings should be same .
Connect voltmeter between battery insulated terminal and alternator's main output terminal. See Fig 5. 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 is probably a faulty diode pack or dirty or loose connections in battery-to-alternator wiring.

Fig 5: Voltage Test at Main Output and Battery Insulated Terminals
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If more than 0.5 volt, check battery-to-alternator circuit .
Disconnect battery ground cable. Disconnect alternator. Connect an ammeter between main output terminal and disconnected output lead. See Fig 6. Connect a jumper wire between "IND" terminal and "IND" lead.

Fig 6: Voltage Test Under Accessory Load
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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 normal charging speed, until ammeter reads less than 10 amps. Voltmeter should read 13.6-14.4 volts. An incorrect reading indicates that regulator is faulty.