Vehicle
Toyota Corolla KE10.
Symptom
Alternator / charge warning light on the dash. On this early system the question is whether the external voltage regulator or the alternator itself is at fault.
Testing
These cars use an external regulator (six wires) and an alternator with three wires on the rear. Later electronic regulators can be fitted in place of the original, but on-vehicle alternator testing stays the same.
With the regulator opened we found the relay was not being pulled in by the alternator. Manually clicking the relay allowed the alternator to charge — which looked like a classic regulator fault. Workshop information showed the relay is a ~6 V relay pulled in by the field (F) circuit. If the F circuit is missing because the alternator is faulty, the relay never closes and the output path never operates.
Repair
Replacement Bosch alternator fitted. Charge light out and charging restored.
Book in
Similar fault on your vehicle? Call the workshop and we will tell you what to expect for diagnosis time.