RCris1985

So about 3 months ago I asked the guru's for some help figuring out if my alternator was shot on my '81. I replaced the alternator after O'Reilly's tested it (with it still installed) and came back with a failed voltage regulator. Since early November I have driven her about a dozen times and noticed that the battery gauge on the dash was acting appropriately. I should mention that I was away on business from the middle of Nov thru the end of Dec. When I returned I checked the gauge again and everything seemed peachy.....until yesterday.

Yesterday I was driving home and she had a hard time starting. I noticed the same low voltage symptoms I had seen when my alternator crapped out on me. I drove her down to O'Reilly's today and the battery lasted until I pulled into their parking lot. I had them test/charge the battery and then test the newly installed alternator. Turns out the Voltage Regulator was once again fried. I had them order a new one because it was still under warranty and would pick it up later.

On my way back to the store I started thinking that maybe the alternator was fine all along. Would the failed voltage regulator code show up if the alternator voltage used for charging the battery was not being seen on the leads connected to the battery? I ripped out the alternator regardless and asked for them to bench check the alternator just to see. Surprise, surprise the alternator tested fine on the bench, showing ~14.7v.

So my question is. If there is a short somewhere that is causing my battery not to charge, where would be the first place I look? Also, would it only be the positive lead I need to worry about as far as the short goes? Is there any reference to how this cable is ran throughout the car so I can get an idea of what I need to check? Or does anyone else have some other ideas why this could happen?

I'd appreciate any input as always.

Thanks,
Ross

wombvette

Check the two wires on the plug for voltage. Both should have 12V. Also check the large wire just to make sure there is 12V there too.

There is a small D shaped hole in the back of the alternator. Ground the little tab to the case with a screwdriver with the engine running and see if it puts out full blast.

RCris1985

It sounds like you are suggesting I test the leads on the alternator itself, correct? If so I actually got a new alternator regardless because I have a lifetime guarentee. I don't believe it's the alternator at all because the bench test came back with passing results. Or are you suggesting I test the cables that are wired to the alternator for the voltages you stated? If that is what you are implying, are you saying that there is a voltage that comes from the battery to the alternator?

Pardon my ignorance, I'm new to the car mechanic world, haha. I have 10yrs of satellite communication experience so basic mechanics and electronics are in my wheel house but cars are a little foreign.

Thanks

RCris1985

Another quick thought that I've heard from random people is the possibility of a fuse being loose or blown. Does this seem to make sense to anyone why my battery wouldn't charge with a faulty fuse?

wombvette

Yes, those wires are powered up all of the time. If you ground the little tab in the D shaped hole, it by-passes the regulator, and the alternator will charge full, if it is good. If it charges then, the regulator is bad.

RCris1985

I'll give that a try tonight after work. If that tests good do you have any other ideas?

RCris1985

So I came home on lunch to check those cables and low and behold, the hot wire on the alternator side was completely corroded and literally snapped in half. It looked like someone had spliced two cables together and wrapped it in electrical tape...obviously not well enough!

So now my new question. Is it cheaper/easier to replace the cable entirely or just splice it like it was?

noonie

You can buy the field/igniton and bat+ pigtails at any parts store.
Easiest is to use a butt or parallel connector and crimp/solder/heatshrink the splices. then cover with tape wrap or plastic conduit for looks.