Originally Posted by patbob

Alternators have two sets of rectifying diodes that turn the AC current into DC. The main set rectifies juice for the battery and rest of the car's electrical system. The secondary rectifies it for the voltage regulator. The alternator light straddles the two sets. When the alternator isn't charging, the current flows from the battery, through the light and then through the voltage regulator to ground. If the light goes on when at idle, and off at higher RPMs, then you know that the alt isn't putting out enough juice at low RPMs, but you don't know why that's the case.

It could be something simple like alt belts that slip a little, or a regulator that isn't contacting so well anymore, so check them. It could also mean the diodes are weak. In all the cars I've owned I've never had to diagnose an alt to this level, and I don't have a wiring diagram for your car, but if I read mine right (and assume yours is similar), with the B+/D+ wires disconnected, and the regulator removed, you can test 6 of the 9 diodes for serious leakage with a battery-powered test light. See if you can light the test light by conneting it across B+ & D+, try both ways. If it glows, even weakly, in either direction, then the alt probably has some bad diodes (or there's so much dirt it is conducting electricty). The other three diodes could be bad, but I can't see any way to test them without opening the alternator up.

Dunno about the meter. There's no way it should have been able to draw enough current to warm the lead wires on a voltage setting.

hope that helps, and please let us know what you find out.