Alternator Pains

Henry T said

The car is a 73 swinger hasn't been much change in the wiring I cleaned up a few not so great looking things and ran a new wire from the alt straight to the guage and then to the relay on the fender getting it away from the fire wall connector.That was a few years ago

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So all was working correctly then something happened?

The way your alt works is...

There is a switched battery voltage feed that comes from the ignition switch.

That goes to one of the field terminals on the alternator. (Blue wire)

The green wire that goes from the other field terminals to the voltage regulator provides a variable ground via the voltage regulator.

The other wire that goes to the voltage regulator provides a voltage signal to the regulator to tell the regulator to increase or decrease the charging voltage.

If that wire has lower than battery voltage that will induce an over voltage charging situation.


With the car running, you need to check voltage from battery negative to voltage regulator positive input and the switched field terminal voltage.

Both should be very close to battery voltage.