With ignition switch off, check voltage at "R" terminal and "L" terminal. Reading at both terminals should be 0 volts. If either reading is not 0, alternator is defective.
Turn ignition switch on but do not start engine. Voltage at "L" should be 1-3 volts. If voltage is 0, alternator and regulator are defective.
If voltage at "L" is close to battery voltage with ignition on, short circuit the "F" terminal to the rear alternator housing. See Fig 1.
Read the voltage at "L" with "F" terminal shorted. If voltage is lower than battery voltage, the regulator is defective. If voltage is close to battery voltage, alternator is defective.
With ignition switch off and battery ground cable disconnected, connect ammeter between alternator terminal "B" and cable. Connect voltmeter between "B" (+) terminal and ground. See Fig 1
Start engine and accelerate to 2000-3000 RPM. Turn on all lights and check ammeter for specified output.

Fig 1: Alternator "F" Terminal Location
Courtesy of NOT AVAILABLE

The terminal is located inside the hole at a depth of approximately 0.8" (20 mm) .

Fig 2: Alternator Output Test Arrangement

Courtesy of NOT AVAILABLE

Illustration applies to all vehicles .

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

Output Test