Voltage Regulator Full-field Test
Perform a full-field test when the alternator has low output and the voltage regulator is suspected to be at fault. This test will rule out the regulator by bypassing it and energizing the rotor with full battery voltage.
The first type of field circuit is the Type-A circuit. It has the voltage regulator on the ground side of the field coil. The second type the Type-B circuit the voltage regulator is located on the power side of the field coil.
Another type of field circuit is controlled by the PCM. This type of regulator controls the duty cycle and is integrated into the PCM. Others (GM) have a tab on the back of the alternator that when grounded to the case would full-field the alternator for maximum voltage. Always check with the manufacturer on the steps required to field test the circuit.
If the alternator produces low voltage and when full-fielded produces maximum voltage, the regulator is at fault. If the alternator produces low voltage and when full-fielded still produces low voltage, the alternator itself is at fault.
