I noticed last night that my ammeter is jumping from +15 to -10 quite a bit, with the lights dimming each time. It is happening regardless of whether the lights are on or not. Would this be caused by the voltage regulator or alternator. How can I test the voltage regulator on the car? Its a 69 Charger, running original points system and alternator.

The reg. A guy (Mrrandy) on here has one that looks OE but is electronic for $28 to your door and this conversion (whoever you go w) is a smart way 2 go as the electromechanical ones are problematic & it could stick closed & full field everything EDIT you could open it up & check the cond of the contacts & not sure what the old manuals recommended to sand them (assuming the prob is in the contacts) if you wanted to chance it. Might b worth a look see

Any good parts store has the electronic ones.Most dont carry the points type anymore.There is an adjustment for the points and I used to use some fine emery to clean them when I had them.They were definetly a weak point on early Mopars.Rocky

Thinkin out loud here, but I have already done the relay upgrade to the headlights, so they atre now getting full power directly from the alternator (not through regulator) and they are dimming as well, so maybe its the alternator and not the voltage regulator? or bad battery?