I recently purchased a 1960 Mark IX at auction. While driving it home (about 50 miles), I noticed the ammeter was on slight discharge. My mechanic detected that the dynamo's polarity wasn't set; he set it, and the dynamo is now charging. But I haven't put the car in service yet. The battery was replaced a few months before I bought the car; I'm guessing the battery had been discharged long enough for the dynamo to lose its polarity.

The few articles I've read on dynamo polarity indicate that driving the vehicle with incorrect polarity can damage the regulator, which in turn allows the dynamo to overcharge, overheat, and destroy itself.

How can I tell if the drive home from the auction did any damage to the regulator? I'd like to fix any problems before I put the car back in to service and do any further damage to the charging system?

Thanks!!

 

Well, we were going to pop open the regulator to inspect the condition of the breaker points, but instead we just put a meter on it. 13.3V at idle, 13.6 at about 2500 RPM. We figure the regulator must be working else the voltage would've been significantly higher, so we're asserting that it's all good. Hope we're right!