Field Open Or Short Circuit Test
Set ohmmeter knob at 1 and calibrate meter as directed by manufacturer. Contact alternator "FLD "terminal with one probe and "GND" terminal, with other probe, then spin alternator pulley. Ohmmeter should read between 2.4 and 100 ohms, and should fluctuate while pulley is spinning. Infinite reading (no needle movement) indicates open brush lead, worn or stuck brushes, or bad rotor assembly. Meter reading of less than 2.4 ohms indicates grounded brush assembly, grounded field terminal, or bad rotor. See Fig 1.