On-Vehicle Testing
NOTE:
Before performing test, ensure drive belt is properly adjusted and all electrical accessories are off.
- With engine off, connect Digital Volt-Ohmmeter (DVOM) across battery terminals. Note reading on DVOM. Start engine and observe DVOM. If reading rises excessively, charging system may be defective or may require adjustment.
- Remove nylon screw from voltage regulator. Run engine at approximately 1000 RPM. Carefully turn adjusting screw clockwise to raise, or counterclockwise to lower voltage to 14.2-14.3 volts. See Fig 1. DO NOT force adjusting screw beyond stop, as damage will occur. Replace nylon screw in voltage regulator adjustment hole to prevent entry of foreign material into regulator.
- If output voltage is excessively high and cannot be lowered by adjustment, the regulator is at fault and must be replaced. If output voltage is excessively low and cannot be raised by adjustment, either the alternator or regulator may be at fault. To determine if the fault is with the alternator or the regulator, go to next step.
- Attach one end of short jumper wire to negative rectifier terminal and other end to a stiff piece of wire at least 1 1/2" long. Insert wire with jumper wire attached into the small hole in the end of the brush holder so it firmly contacts the terminal of the outer brush. See Fig 2. With engine at fast idle, observe DVOM. If output voltage rises, the alternator is okay and a faulty regulator is indicated. If output voltage does not raise, alternator is at fault and will need to be repaired.