Alternator problem??? please help..

I own a 1983 Vw rabbit GTi.... when i was driving home one night, the red light for the battery came on, so i popped the hood to check the belt tension (since it had a history of coming undone) but the tension was just the way it should be. the light then procedded to flick on and of apprx. every ten minutes. i drove to a friends house and he said the regulator in the alternator was gone and that i should make it home no prob. (20 mins drive) i did make it home and then i took the alternator off and went to the parts store and got it tested, they said it should be fine, so i reinstalled it thinking the connction may not have been to great, the next day i didnt drive more then 20 mins when the light went on again.

The volts go to apprx. 11, and stay there for a while, lke half a hour... adn occasionally pop to 13 volts. they will slowly drain to around 10 volts...then i stopped driivng... what could this be?? the light in the dash does not always light up (the red battery led) but the volts are under 12.

Any help would be greatly appreciated!

oh i just remembered... it will work after it has been cold started... it works for like 20mins.

Sounds like a voltage regulator problem. AFAIK, the voltage regulator for your car is mounted on/in your alternator. The regulator can be purchased new for about $25, and is a 15 minute installation task (no belts to loosen, no alternator to remove, etc.).

I experienced the same thing. Read the thread I started under the subject heading "Engine dies shortly after a jump start". It should provide some insight, thanks to the knowledge of some of those who participated in that thread.

Did you pull the brushes out and see what's their condition while you had the alt.out? Even though it tested good on the jig I'd say it's the brushes. You don't need to take the alt. off the car, Replacements are cheap. Ten minute job.

Agreed. Check/replace the brushes.

the regulator was checked.... but since it kept going on and off, i don think the machine would catch that, so ill replace that.. and what would show if the brushes were worn? and i do have 2 exra bosh alternators (mines a motorola) would they fit? both are 65 amps. thx a lot!

If your GTI has A/C then you may have a separate ground strap to the alternator. Those straps sometimes break so please inspect and replace if necessary.

If you have a 3 wire plug that plugs into the socket............sometimes the terminals inside become loose and corroded and need to be cleaned and retightened. Or sometimes the entire plug needs to be replaced or bypassed with plain female terminals of the correct size.

later, dave (One out of many daves)

I second making sure your ground strap is good. I had an alternator that charged just fine. I replaced the worn out rubber bushings and it stopped charging properly. New ground strap and all was good again. It was getting a ground because bushings were shot. Good bushings isolate metal to metal contact.

They would be too short and not within specs for the length.

This reminds me of a problem I had, which is also worth noting. My '84 Scirocco stopped charging on the 401 between London and Hamilton, Ontario, in late 2000. I thought initially it was the alternator, but when I got it home I discovered something else. The alternator sat low enough on that car that road crap was always kicking up on the plug. The wires were all tight and felt fine in their sheath, but when I yanked just a little, the whole plug came off in my hand. The wires themselves, once I cut away the outer sheath, were all corroded back to about 3" from the plug: it was like touching copper dust. Copper dust, it turns out, is a very poor conductor ;-)

I had a similiar problem on a '82 Rabbit - The warning light came on and the local auto parts stores (both autozone and advance) both tested the alternator and said that it was fine - As it turns out the alternator has a post on the rear to which a grounding strap is to be affixed. On the alternator in question, if one attached the ground strap to the appropriate post the warning light would come on and the battery would not charge. If one attached the same strap to any other part of the alternator, the alternator would function correctly. In my case I merely disconnected the oem strap and connected a different ground wire from the bolt that one tightens when tightening the belt, to a bolt on the frame (in my case the radiator support) and all was well. As an aside, I put this same alternator into a 83 rabbit and had the same grounding anomoly when attaching the oem braided ground strap to the grounding post on the alternator, and the same result when grounding it at the tightening point