The alternator warning light on my 94 GXE comes on intermittently...sometimes dim, sometimes bright, sometimes not at all. I replaced the alternator last year (summer of 2002) and everything had been fine up to about a month ago. I removed the alternator and had it checked out where I purchased it, checked O.K. I also checked myself that 14.5V is delivered to the battery. Checked belt condition/tension and pulley, no problem there. The weird thing is, the car starts fine, runs like a top, none of the items that load the electrical system (A/C full blast, lights on bright, stereo cranked up) are affected. I also had the battery checked out...spec gravity + charge w/in normal limits. I was wondering if the light has a sensing circuit that may be bad or some other electrical "gremlin" is the cause. Any ideas?

 

That's the problem, unless you check the alternator voltage when the warning light is on, you will never know exactly what's going on. You have a intermittent problem and the in the electrical world this is the worst kind of problem to diagnose properly. Until it fails all together it's just a guessing game. Brining the alt to be bench tested it isn't subjected to the same conditions as under the hood after being driven for a couple hours. You see where I'm going. Just because you changed the alt in 2002 doesn't mean it can't be bad in 2003, heck just because you changed it last month doesn't mean it can't be bad this month. Again you see where I'm going. Buying a alt from the local parts store is just like rolling the dice, sometimes you get lucky sometimes you dont. That's why I'm hoping my OEM alt never craps out or else I will have to get use to R&R the alt and using the life time warranty. You can change the alt now or wait until the warning light is on constantly, hopefully you have a battery with a high reserve capacity rating. And to answer your question I dont believe there's a seperate sensing circuit for the warning light, it's all internal in the alt along with the regulator.

 

When I had my Sentra, the same thing happened to me. My OEM altenator went out at 146k. Purchased and installed one from Advance Auto and all worked find--for about 3 weeks! Another altenator from Advance (using the lifetime warranty of course) lasted the rest of the car's time. Rebuilt altenators can--and will--go out. Like CandiMan said, it is a roll of the dice.