Battery Light On - 86 Jetta idi

[vwwv]

Was on a 500 mile trip.  No problems on highway.  Got into town and battery light came on.  Thought it might be alternator failure so I went to Auto Zone and their meter said alternator was putting out 13.5 volts and 84 amps but "said" there was a wire disconnected between alternator and battery.  I checked these out and they were okay.  Remanned alternator available @$185 and 4 day delay.  I bought a new battery and headed back on the road for the return 500 miles with the new battery in the trunk in case it was needed.  It wasn't.  I didn't use lights or a/c or radio using the battery only (I suspected) to keep the fuel shut-off open and it ran fine.  Actually, the battery light went off about an hour after I got up to highway speed.  Toilet and one fuel stop (to buy some of that lower priced NC fuel) was done with the engine left running.  What gives?  Bad Battery?  Failing alternator?  Wiring failure?  BTW, I had installed a new alternator belt two days before I left on the trip.  It was not slipping.  Any ideas anyone might offer will be gratefully received.     I am a newbie on this forum and I'll try to be a good member.    Paul

[andy2]

anytime that my battery light comes on the and acts up , its usually one of the two small wires that is either broken or has a bad connection , also follow them back near the battery where they plug into the harness the plugs connection could be the issue itself  :wink:

[vwwv]

Thanks Andy2,  I checked the two small wires (red and blue) for continuity between the alternator and the pull-apart connector near the battery.  They show no resistance.  I went to Advance Auto this a.m. and they used their machine to test the voltage and amperage output. Voltage was 13.89 and Amperage was 86.  That seemed to me (and the tech) to be within parameters for an altenator with over 100, 000 miles on it.  It is still a mystery as to why, when idling there is a very faint glow to the battery light but when a load is applied at idle (e.g. lights, radio, a/c) the light goes completely off.  My primitive intuition is that if there is a load applied at idle the battery light should turn on and at higher rpm the light should turn off?  However, as long as the battery is maintaining a normal charge I believe I'll let sleeping dogs lie.  Thanks again, Paul

[dieselpower]

hey,
mine does the same thing, with the battery light glowing faintly at idle. and i've seen more than just mine that do it.  I think that because there is no load on the alternator and its at idle there is no need to be charging so it halfly shuts itself down. and then when there's a load and it needs to be charging it comes back on.  anyway another thing could be water. i have a hole in my firewall that i've ran wires and stuff through and whanever it rained all my electronics would get screwed up. as in lights working, lights not working, and just other crazy things. anyway i've waterproofed that all now so it's good to go. its just a suggestion.
i hope you get it all figured out.

mark

[vwwv]

Mark, thanks for responding.  I've always been intrigued by the town name "Medicine Hat".  The latest is that I removed the voltage regulator and inspected the brushes.  They are supposed to be no less than 3/8ths inch long.   The "inboard" brush is slightly shorter than 3/8ths.  I had to go out for a short distance after dark last night and the battery light began to flicker on and off and finally just stayed on.  I'm beginning to think there is a dead short somewhere.  Thanks for the idea about water intrusion.  If I can't find a short, I think I'll start by replacing the voltage regulator @ ~$30.00 vs. remanned alternator @ ~ $190.00.    I'll post my results when I achieve them so that others might benefit.  Paul

[dieselpower]

when the light comes on does it stop charging? like was the light still on when you were testing it? because a while ago when i still had my old alternator, before i removed the airconditioning, i had a problem where it would stop charging for a while then stop then charge then stop and so on. the battery light never came on tho while this was happening. when i took it apart the one brush was below the recomended length. anyway i just swaped it out with another regulator with decent brushes and the problem went away.

anyway ya medicine hat is a wierd name for a city. i guess it got it's name for when the indians were here the medicine man was shot and his hat fell in the river. haha thats what i heard anyway. its a little off topic but i just had to share.

Mark

[vwwv]

Mark and Andy2,  my mechanic got back in town today and he thinks the problem relates to the brushes in the voltage regulator - just as we have been suspecting, eh Clouseau?  I took the regulator out of my 90 idi/na and installed it in the 86.  The battery light went out.  The brushes from the 90 are worn down more than the 86 but they work.  Might be some other component of the regulator?  Mechanics volt meter registered only 12.75 whereas the Auto Zone meter had read 13.8.  So, IF the alternator was putting out less than it should, the battery would require charging, ergo the battery light came on until highway speed would produce enough voltage to charge the battery.  I'm going to run these brushes for a few days and if the light stays out, I'll report back.  Thank you both for the responses.  Off topic Mark - neat story about the hat.  I'm going to Google that.    Paul

[fatmobile]

These VWs are notorious for having bad ground connections.
 Is there a ground strap from your alternator to your block?
 Where did you measure the voltage at?
 Check for a voltage drop between alternator and ground.
 I like to run a fat wire from the alternator frame to the negative post on the battery.

[81rabbit]

vwwv...

I was curious if you decided the brushes were the root of your problem or was it something else?

[vwwv]

81 Rabbit - No resolution to the problem, at this time.  The car is hibernating in the deep freeze while I am in post-hurricane Fl.  I will address the problem in the spring when I return to WV.  Thanks for your interest and I will post the results of what I will do once I do it.  Regards to all and Happy and Healthy New Year to all, Paul