I installed a volt meter inside the car and watched it while I was driving. When the battery light comes on the voltage does not change at all. It's right about 15v the whole time. I'm using an analog meter, so it's hard to tell exact voltages. but it's accurate within a volt or two.
I connected the meter between engine ground ( right behind the alternator bracket ) and the + battery cable at the alternator.
I tried re-creating the problem by wiggling the wiring harness around, but have failed to do so :-/
Still looking for a solution