Open Field Or Short Circuit
- Perform test before alternator disassembly. Adjust ohmmeter to lowest scale. Place ohmmeter leads on regulator terminal "A" and regulator terminal "F" screw heads. See Fig 1. Rotate alternator pulley and note reading. Reverse ohmmeter leads and repeat test.
Courtesy of FORD MOTOR CO.
- Reading should be 2.2-100 ohms in one direction. Fluctuation may occur while pulley is turning. Reading should fluctuate between 2.2 to 9.0 ohms with leads reversed.
- A reading with approximately 9 ohms in one direction and no continuity in the other indicates open brush lead, defective brushes or loose regulator-to-brush holder attaching screws.
- Reading of less than 2.2 ohms in both directions indicates a shorted rotor or defective regulator. Reading exceeding 9 ohms in both directions indicates a defective regulator or loose terminal "F" screw.
- Place one lead on alternator rear housing with remaining lead touching regulator terminal "F". Note reading. Reverse leads and repeat test. Reading should be infinite in one direction and approximately 9 ohms with leads reversed.
- Reading less than infinite in both directions indicates a grounded brush lead or defective regulator. Reading exceeding 9 ohms in both directions indicates defective regulator or terminal "A" connection.