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General alternator /charging issues


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Hello all --

I'm hoping some 2002 guru can help me. I'm having problems getting a full charge from my alternator. (I've got a 71 2002).

First things; I have a brand new 45 amp bosch alternator. I also have a brand new Sears top of the line battery.

My problems started a couple of years ago; my alternator got fried somehow. The wiring harness basically melted. I replaced the alternator with some mail order unit, and my friend and I basically kludged together the wiring by stripping the wires and putting new direct connectors on them. I also ran a small ground wire to engine from the alternator.

Anyway, it would never seem to fully charge the battery and my battery was constantly dying or dead (and the battery was junk anyway). So anyway, I replaced both the battery and the alternator, but I'm still clearly having problems because the car died on me yesterday and I've been getting the dreaded red light when idling.

So first things first; is it possible that we screwed up on the "replacement" harness? We did our best to make sure each of the three wires went EXACTLY where they had entered before, but perhaps we messed something up?

I don't really know how to test for amp output. What do I need to do this? How do I go about doing this?

Is there any way to get a replacement harnass? When I go to junkyards, they've just scrapped them.

Please help!

Thanks so much,

Richard Huffman


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It's possible your voltage regulator is not working. When you say you replaced the harness with direct wires, I'm going to guess your talking about the 3 wires on the back of the alternator, that basically go straight to the regulator. Those 3 are easy to check with a meter set to ohms. If you pull both plugs, they have letter T shape sort of. Each pin in the same place of the T should read 0 ohms from regulator plug to the alternator plug. Besides that, there is a small wire from alternator to the engine block, about 12 or 10 guage. You should read 0 ohms from case of alternator to engine block. You also have a ground strap from bat to engine block & to car body. Make sure those connections are good, have a local store test the alternator, or try another voltage regulator. Also check screws that hold regulator to car body, clean and or tighten those.

You probably don't need a new harness, if all that got melted was those 3 wires going to the regulator. You can find a used harness on the parts forum maybe, there are front & back sections to the harness. I'd try to fix what you have before replacing a harness, that might make for more problems. I think new harness is NLA.

Hope that helps.

2002 owner since 1980

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+1 on the grounds. These can and will screw with your charging system, and the stock wires may prove to be inadequate when faced with higher amperage than stock even if they're in good shape. The ground from the alternator to the block is often forgotten, but vital.


Just because you're not paranoid doesn't mean they aren't out to get you.

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We put a big fat ground on it a couple of years ago; but I'm going to check the connections just in case. I discovered the electrical testing FAQ on this site and it is extremely straightforward, so today I'm going to get a multimepter and test things out. I'll bet the supposition that its a voltage regulator problem is correct, but I should know by the end of the day...


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Hey all --

I wanted to give a quick update. Thanks to the EXCELLENT instructions on examining the charging system in the FAQ section by Chris Blumenthal (I'm really a neophyte and they were incredibly easy to follow)...

I've narrowed things down a bit. At the battery, I am getting 12.8 volts or so, which is apparently good. So I checked at the alternator and I was getting about 12.5 volts at 1000 RPM, and maybe 13.5 at higher revs. Not good. It occurred to me that perhaps my fan belt either wasn't tight or is slipping. I tightened things up, and it got a bit better, but not enough. Being that tomorrow is Thanksgiving, on Friday I'm going to get a new fan belt and see if that makes a difference (it was too dark to totally examine the thing, but I've never changed it in three years...).

So right now I'm operating on the assumption that the fan belt is my problem... does that sound plausible? I have a brand new bosch alternator on the thing and a brand new, top of the line battery, and since the multi-tester shows me the problem is at the alternator I can only assume it was the belt...

Also, if anyone has any recommendations on fan belts, I'm all ears. Should I go to Bow wow wow German automotive, or just my local Schucks? Does it matter?

Thanks all..

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13.5V alt output is not so bad. Did u do the regulator check on Chris's faq?

Is your red light glowing only at idle? What is your idle rpm?

Can you see if the alt belt is slipping? Can you turn the fan easily (with the motor off course) without appreciable belt resistance or the motor trying to turn?

Get a good belt if needed, the cheap ones may not be able to handle high rpm as well.

You might examine the alternator mounting bushings as well.

If alt output is 13.5 at above idle, I'd check and replace if necessary, the ground and positive cables (assuming the connections have already been checked and found ok).




Stop reading this! Don't you have anything better to do?? :P
Two running things. Two broken things.


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