Hi all. 2003 w/80000 miles. Recently the alternator light has been coming on for short periods(a minute or 2 at the most) while I'm driving. It doesn't matter accessories are on or off. I hooked up a "scan gauge" to display volts and water temp along with rpm. At rest car off, 12.9v. Start car 13.6 to 14.0 volts.(car is cold) Turn on A/C (or rear defrost or seats) volts drop to 13.4 then recovers to 13.6-13.8. When the car is warm 195/205 deg. the output falls to 13.1-13.5 based on rpm. When the dash light comes on the volts will still increase but only .1 or .2 volts. The light seems to come on more when the high speed cooling fan kicks on. I've done some tests, i/e test lead from + to B+ on alt. and it is a little high, 0.5 volts (one book said it should be 0.2v). The - test, a ground point to alternator case is 0.2 volts. My question is are there any other tests I can do while the alt. is on the car or any way to test the lamp circuit? / Fan motor? Or... just let it go until I get a steady light and the car leaves me stranded,ha-ha. OK, thanks in advance for any input.

 

Sounds like your alternator might be going out or has some issue. Hopefully it will totally fail before it drains the battery. Have you had the battery tested? If the alterantor dies, you should be able to drive 20 miles or so on a good battery.

 

Yes the battery is good, but what is throwing me is that the meter is showing an increase of volts with increase of rpm but the light still pops on once and a while. Oh well, so far it's maintaining between 13.4 and 14.1+/- depending upon ambient temp and engine temp. I'll just keep an eye on it . Thanks.