93LX5.0L5SpdConv

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?

mjr46

good you replaced the plug, there was a recall on those back in the day and new harness ends use to come with reman alts, not sure if they still do, also don't trust that vatozone test at the store, you have to catch the prob when it occurs and most likely when it was tested at the store, prob was not present, as it heats up things will go to open circuit, coupled with underhood temps, the prob will be amplified, replace alternator as well!

93LX5.0L5SpdConv

That makes sense, charges OK on the open road but drops off when there's less air flowing under the hood.
Thanks mjr

93LX5.0L5SpdConv

New alternator in place for 3 days now, running and charging fine - on the open road and around town getting good and hot under the hood.

mjr46

good deal

Car collector

I see you replaced it all ready, but for future reference I had the same issue on my 93 notch. turned out to be the voltage regulator/brushes in the alt... Replaced those and it has been charging fine ever since.

93LX5.0L5SpdConv

I thought about that, and if I hadn't needed it the next day to catch up on work I'd missed the day and a half before, I would've tried that.
What I really wanted to do is upgrade to a higher amp alternator...

yurizx6r

I just recently did the 3G alternator upgrade. It was pretty easy and straight forward. Latemodelrestoration.com has a kit you can buy with everything you need to do the upgrade. They also have a video to show you what to do. I personally think it's worth it, and you get the added benefit of getting rid of the external "cut your finger off" fan on the stock alternator.... drove my OCD crazy! lol If you have not replaced the alternator already, it might be a good upgrade and replacement thought. Just be sure to buy the wiring kit to do the upgrade properly. But if you're a baller on a budget, junk yard baby!