One of the tests we used to do at the GM dealership was what we called "full-fielding" an alternator to check output. To do that, we simply stuck a small metal object such as a nail into a small hole built into the back of the alternator. The "nail", when touching the side of the hole, and what I'm thinking was a spot on the regulator, would cause the alternator to go to full output, dragging down the car engine
considerably.
This was to be done only for a couple of seconds, to prevent damage to the alternator or car's electrical circuits. We did this to help diagnose if a problem in charging was internal to the alternator, or somewhere else.
What I'm wondering now is if this was causing the generator to go to a higher voltage or full amperage. I never did do it with a meter attached to find out for sure, as I can remember. I'll have to play with my son's GMC to find out what it was...
