It'll start and run fine, some times for days, then I see the gauge bouncing from where it should be down to just over 12 and then drop to right at 12, then lower and the battery idiot light comes on. I pulled the alternator and it tested fine at the parts store. I cleaned the corroded top 3-prong plug and it was good for a couple days. Then the same symptoms and I replaced the 3-prong plug. Worked fine for several miles now the same symptoms again. If I keep it well over 2000rpm the idiot light shuts off and the gauge sits just below 12.
WTF?
WTF?