Alternator giving me fits!!

[Jules823]

Ok I am working on a restoration project for a customer and I'm having a pretty good amount of trouble dealing with the electrical system.

When he bought it, they said it needed an alternator. So I replaced it, and for a short while, it was doing great. It had over 14 volts at the back of the alternator and at the battery. But after a few months, I noticed that it's output had dropped to just over 1 volt. So I replaced it again under warranty, and it had no change. I even went as far as to replace it AGAIN, just to be sure, and the results were once again the same.

I suspect that maybe the plug might be faulty. The wiring to the alternator appears to be "messed with" and it might even be spliced in a few locations.

So, on to my question: Does anyone know what could cause this?? And if I were to rewire the alternator circuit, where could I find some info on how to do it?? I need to know where to tie in what wires and all that good stuff.

Thanks in advance for any help/advise.

1986 345
454 gas engine

[HowieE]

Have you tried a different battery on it? Sounds like the battery may have a short internally and not applying voltage to the alternator.

I have suffered the same problem.

Also check the voltage on the small wire at the alternator that should be hot when the ignition is on. That is what excites the alternator. Depending on the age of you rig there may be a fuseable link between the battery and the alternator in the heavy wire. Check that wire for continuity.

[guy99]

If the house batteries are down (or shorted) they can burn out an alternator fast. Also, you could have an isolator problem. This thread has some information about my experiences:

http://www.airforums.com/forums/f159...rce-21067.html

I'm sure the guys I got my alternator from could help your verify/correct the wiring.

Also, this guy has lots of OEM connectors:

Automotive Repair Connectors And More

[mustang]

When you replace an alternator you should always make sure the battery is fully charged. Whatt it sounds like to me is you are useing autozone parts. When the regulator weakens it does exactly what you are describeing. If you have voltage everywhere without a drop I wouldnt touch anything. Did you bench test the alternator when you took it back? That might be a tell all answer. I HAVE RUN 3 SEPERATE TESTS ON AN ALTERNATOR 1 RIGHT AFTER THE OTHER THEN ON THE FOURTH TEST IT SHOWED AN IRREGULAR DIODE PATTERN. Sorry for the caps. My paws dont work good with these Keys. I hope this trouble shooting helps

[Jules823]

No I'm using OEM parts. I really don't think it's the alternator.

I really think it has something to do with the two wire connector that plugs in.

Does anyone have an experince with the wiring, or should I say RE wiring of these GM alternators.

[mustang]

Another thing you could do is disconnect the positive cable of the battery put a meter between the 2 (positive cable and battery post) see how big of a reading you get. then if it is big disconnect the alternator and read again, if reading drops then ya there is a short. or wireing issue.
Inside an alternator is pretty simple trio diode brushes windings voltage regulator. Wireing outside is a little more complicated but you can trace the wire as far as you can then splice in a peice. make sure you use shwrink tube to seal out moisture other wise you repaire wont last very long. I am a big one on soldering connections also

[overlander63]

Originally Posted by Jules823

No I'm using OEM parts. I really don't think it's the alternator.

I really think it has something to do with the two wire connector that plugs in.

Does anyone have an experince with the wiring, or should I say RE wiring of these GM alternators.

Rewiring the old GM internally regulated alternators is very easy. I just wish I could remember how to do it...
Seems like cutting off one wire of the two, and running the second wire to the output post of the alternator.
I've done dozens of them that way, but it's been a long time since.
I'll post again if I remember for sure, but it is very simple to do.

[overlander63]

Okay, here it is, with a diagram.
Terminal 1 is switched battery voltage, so it can be powered when the key is on.
Terminal 2 can be wired directly to the charge post on the alternator.

[richinny]

so Terminal 1 only works the idiot light?

p.s. i remember to test the regulator, there is a hole in the back case with a tab inside, that when grounded to the case, gives you full alternator output.