Alternator exciter wire question.

[offalot]

For a while, in order to get my caddy charging ie. cut off the red battery light, was to rev the motor to rediculous RPM. This is a pain, as I don't like doing it on a cold motor and there is a chance I can forget. I never reach this high of RPM while driving, so it hs to be purposefully. So I understand it has to do with the exciter wire. I've read a bunch of threads on it but usually they deal with something not working at all. Mine works, just at a different rate. It's been like this through 2 alternators, so I don't think it's in the alt. The light does come on, so it seems the LED is good. I haven't checked the resistance of the wire yet. I have the cluster out now. Can anyone point me in the right direction as to what to check on this?

[82vdub]

I've had a similar charging issue with my winter gas Jetta this past winter. I'd be driving, and then the car would start to miss (not moving enough fuel) and the tach would get all weird. Anyways, it has to do with that little wire going to the alternator through the red light on the dash.

I believe the purpose was that if the red alt light burned out, the alternator wouldn't charge the car, so someone would get stranded, have a $100 towing bill, but they'd (hopefully) find out that the $.35 light bulb burning out was the issue (if the repair shop would even find this out). Well, maybe it's not as bad as I make it sound, but it seems pretty stupid that the car wouldn't charge if the alt light in the dash quit working, but that seems to be what happens.

With my car, I didn't know if the wire had a break in it, a bad connection, or if the alt light burned out. I rigged up a voltmeter so I could tell if the car was charging, and after a couple days, I determined that the alt light worked, although intermittantly at some times. So, a connection on that little wire may be bad, or there's a short in the line somewhere.

I never did end up working this out, as the problem seemed to go away. The previous time I got stranded was two winters prior, so it wasn't happening very often. However, I did spend some time at my local starter/alternator rebuild shop. There is a "one wire" voltage regulator that's available for the VW alternators. GM went to the one wire setup long time ago (maybe everyone else did too), so for the $35 regulator and time it takes to swap it out, your charging issue could likely be eliminated in your case. I know this doesn't solve the red light being on the dash issue, but it will likely solve the charging issue. The only other item that I don't know the answer to yet, if you use the one wire regulator and the alternator quits charging, will the red alt light come on?

[offalot]

Man wish I knew about that regulator before. I just replaced one for a spare. Where do you get These one wire deals?
So back to the light. My understanding us it connects the aLT. To s ground once it users a charge. The Bentley just shows the LED in line from the alternator to ground so I am a little unclear on the operation and how it could be causing my symptoms.
All I could think I'd the wire may e frayed enough somewhere to allow enough juice to light the led but not kick on the alternator.
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[Fatmobile]

What kind of alternator?
Rectangular (motorola?)regulator or round.
Rectangular? take it off without snapping the small bolts, clean where it contacts the body of the alternator.
And of course,.. put it back together, ha.

[82vdub]

Where do you get These one wire deals?

My only source for this information was a local shop that specializes in rebuilding starters and alternators. He looked throught the book of regulators that they can get, found a listing for a one wire unit, called their supplier or warehouse to find out if he can get them and he could. I don't know any more than that. If you can find the name of a company that makes voltage regulators, they may have a website that you could get more info from, or find a local rebuild shop in your area.

[TylerDurden]

While the cluster is out, I'd check the blue wire continuity to the connector at the cluster, and continuity to ground.

AIUI, the diode and blue wire supplies a trickle of current to the alt to energize the field. Once the alt generates enough current to self-energize, the field no longer draws current through the diode and it no longer glows.

If the diode glows, current is flowing through the diode to ground somewhere. If the alt takes extra revs to self energize, not enough current is reaching the field. So there may be a leak to ground sucking the juice away from the field... maybe in the harness, maybe in the regulator.

[offalot]

Well I took that info and messed around with it, I thought I had found a direct short to ground when I tested the plug in the cab, but between losing light outside and using a piece of crap voltmeter, I think I was fooled. I am going to borrow a good Fluke meter and hopefully get to the bottom of this here soon.
I did test the continuity of the D prong to the alt. body and was getting somewhere around 3 ohms. Tried it on the alt. that I just replaced the rectifier on and got close to the same. Not sure what that means. Hope I get this figured out.

Oh, and I had a thought that kind of makes sense (I think) with your diagnosis. When the car is off the battery light glows ever so slightly. Also, not sure how related it is but once I rev the crap out of the motor and the light goes out, my oil pressure light flickers a little (I don't have the oil wire hooked up, as I run an aftermarket) Man I wish I had a better grasp of electrics.

[TylerDurden]

A Fluke might be overkill, but a flaky meter is worthless.

To clarify my previous post, I'd check continuity on the exciter wire while it's disconnected at both ends. Same for checking shorts to ground.

It is common for the wire to break in the bend near the alternator, but the insulation on the wire may still allow the broken ends to barely touch making a diabolical intermittent condition.

If the light is glowing at all when the key is off, something is leaking voltage into that circuit. Anyone install goodies like stereo, alarm, gps, NSA microphones, etc.?

To test if the alternator is ok, I'd put the DMM probes on the battery terminals and run the engine... should be ~12 before the alternator charging kicks in... then jumper a wire from the battery positive (or the big cable on the alternator) to the exciter terminal on the alternator... the alternator should immediately start outputting ~13.5-14V.

That jumper can even be a line into the cabin for a temporary manual kick until the problem is solved. I sometimes also run a line into the cabin to a cheap DMM (velcro-attached) for a temporary voltmeter.

[offalot]

Welp, I figured it out. Get this!
I tested the detached wire and there was no continuity to ground. The other night I misread it and thought there was so I hacked into the harness a bit, so after repairing all my screw ups, I continued. I inspected the cluster, no visible problems. I even threw another spare cluster in there, same results. I ran the hot jumper wire and tried to trigger the exciter. No dice! So it seemed to be the alternator.
As I was replacing the Bosch alt. with the motorola I "rebuilt" I noticed it went on a bit easier(I'll get back to that). After getting it all installed I tried it out and blipped the throttle, 13.4V!! Yay! SO getting back to the easy install. I measured the pulleys on the two and found that the motorola's is 2.7" and the bosch is 3.1" so like 13% bigger or the difference of almost 500 rpm around cruising speed.

As I was typing this and thinking I cracked the code, I realized the info doesn't correlate. If the pulley size was the main culprit than the bosch alt. would have still kicked on when I jumped the exciter. Hmm, guess its just a crap O'reillys alternator.

Thanks for the help though!!