Accepted Answer

Hi Dogbone,

Here's my advice. Um, 3 bad alternators in a row? Probably easier to hit the Pick 4...

This is easy to test:
1) Battery is fairly new but it keeps getting run down. So, you'd want to trickle charge it now, as needed, to bring it to capacity. OK? You need around 12.6 Volts, static, engine off. When loaded to half its' CCA rating, (load tested) you need to hold at about 10.8 Volts, or above, for about 15-20 seconds. An automated tester (like a free test, at say a "chain" automotive service center) will give some more detailed info. Like the amp capacity, battery state of charge and state of health, etc. Point is this, at least charge it up! Cannot test Alternator Output with weak or dead battery. The alternator should be able to maintain the battery at least 13.2 Volts at idle engine running. Better still, it would be nice to see 13.5-14.2 volts - ideally. We can see 14.5-14.8 (ish) on high side, before we're over charging. NOTE - Some newer cars are real advanced. The PCM regulates charge. With engine hot, it may bring output down LOW. Lower then what many know. Some cars can charge as low as 12.8 volts at idle engine hot and no acc's on. Weird huh?

OK, so all this is background info. It helps us 'base' test. But an obvious thing to do after 3 alternators - Check POWER Supply at back of Alternator. Check GROUND. Have you 12 volts at main, single wire, that's thicker then the others? (higher gauge for high amp flow, generally at single lug with plastic shroud and/or cover). We need 12 V there to have a system charging. Also, is alternator grounded? Simple 'cheap' test, a test light. (pls do not use test light for regulator testing or any computer testing) Place the test light clamp to battery positive (yes positive) and then probe Alternator CASE (if no black ground LEAD is bolted to CASE) Does light illuminate? If so, you're grounded. If there's a black LEAD bolted to CASE, test that connection directly. My point is, to go further, we need a good battery and need to know the alternator has power and ground. If it does, start engine. If the voltage stays around 12-12.6 volts or even LOWER - you have NO output and I can tell you what to do next. If you DO have output - then I can tell you what to do. But - the test for each scenario, is a totally different test. If you accept this I will stick with it on follow up (related) procedures. OK? :)

Best,
Master Class

Expert:	Master Class Auto
Pos. Feedback:	100.0 %
Accepts:
Answered:	8/9/2009

ASE Master Technician

20+ years, full time experience. ASE Master Tech. Specialize in Diagnostics & Electrical