HELP! 86'Firebird 2.8 won't charge more than 12V

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As someone else mentioned, make sure the alternator is grounded. I have seen the brackets not ground a lot of times over the years on GM's. You can check that by taking a booster cable and running from the battery
negative to the alternator case to see if it turns on.
My 86 Jeep runs the same GM alternator and it gets it's excite power from the coil power wire just before the ballast wire (on the 12 volt side).
I also have seen this same alternator have the wires switched on the small white plug on the alternator. Some versions have the A and B switched for some reason on different years of Jeeps anyway.
Maybe your harness is for the other version of the alternator and those two wires are in the wrong places?
Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's
Gil wrote:

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What are you using to measure the voltage? Joe--ASE Certified Parts Specialist & 10th Ann.Club Tech Director '80 Carousel Red Turbo T/A, 26k orig. '79 "Y89" 400/4 speed 10th Ann. T/A, 57k orig '84 Olds 88 Royale Bgm 2 dr, 307 "Rocket" (lol), 141k and still going.... '80 T/A project car...
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snipped-for-privacy@aol.com (Bigjfig) wrote in message

Anologe VOM. It matches fairly close to the volt gauge on the dash.(see previous post) Its got a mirrored scale & needle that you have to be lined up with on you eye sight ok? so error is +-.25 volts? Its the old fashon kind. I opened up the hood on my Lincoln LSC & read 13.5 volts with lights on. Its not the meter.
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Gil wrote:

Ok.
Now look on the back of the alternator case for the plug numbers on the white plug.
The small brown wire needs to be on pin 1 on the case side and the red wire on pin 2.
I have seen the pin numbers on the alternator be opposite on some so the brown and red wires need to be swapped in the plug. They come out of the plug by pushing on a tab with a mini screw driver if needed.
The brown wire is on top on mine, my old tenant had his on the bottom.
Also the place to check for output is right on the alternator bolt for the big red wire and on the alternator case. That gives a reading off the alternator not off any wiring that might be bad.
Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's
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hoohoooooooo!
Ya think somebody or some instuction sheet could could have mentioned that when the Alt. was bought?
Car now F/S not to bad for an 86 f'n bird.
Thanks all for your help!
Gil
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Gil wrote:

You are welcome.
It is a strange one though isn't it?
I figured this out by helping folks with Jeep wiring. Jeep uses the GM alternator for a mess of years and with all the mixing and matching folks do on old vehicles...
Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's
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Well, the only thing I'm wondering now is, the volts are not droping back down to around 12.5,only for a r short time after the first start. After that its staying up at 13.5+, even with all acc. off. Hmmm. maybe be overcharging now? getting a draw somewhere? or we weakened the battery by draining it down to many times? So far its running & the kid has not called home to come & get him.
Thanks Again!
Gil
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On 3 Jun 2004 18:56:12 -0700, snipped-for-privacy@cin.net (Gil) wrote:

Dropping down to 12 would mean a problem. 13.5 volts is about right in most cases. Usually should be between 13 & 14 volts from the alternator I think.
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Gil wrote:

That sounds normal. Depending on the state of the battery, my alternator varies on the gauge between 13 and 14.5 volts.
Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's
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Great catch on that Mike!
I couldn't have done that without having the parts in my hand in plain sight!
Congratulations for being a long distance diagnostician!
Refinish King
You Da Man!

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Actually...it better NOT drop back down to under 13 when running...or you have an issue again..

It sounds like its fine....

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