1990 1.6TD Battery Light is ON, but Battery is still charging.

[vwjets]

My first time posting on this forum.  

I've been to VWVORTEX and TDICLUB and can't find my situation posted anywhere.

My alternator stopped charging and all my electronics started to fail (headlights dimming, wipers wiping very slowly).  I could start the car with a boost or by bump start and the engine would run.  (Just enough power in the battery to keep the injector pump activated)

For some reason, my alternator's blue "exciter" wire failed and was replaced.

As a temporary measure, we tried connecting a (blue) wire directly from the alternator's + terminal to the battery's +tive terminal.  The alternator started smoking!!

So we spliced the replacement blue wire into the harness that runs to the dash.  The other wire is the red/black wire from the W terminal.

Now, the system is charging at 13.5V, the electronics work fine, and the tach reads the RPMs accurately, but the "battery" light is on (and it's bright), despite the system seemingly charging properly.

I'm thinking the dash light is short circuiting somewhere... but I can't figure out where that could be.

How should I troubleshoot this?

[Vincent Waldon]

Smoke from an electronic device is rarely good... since they run on smoke, and if you let the smoke out...  

The easiest way to troubleshoot the cluster and blue wire part of the charging circuit is to:

1) disconnect the blue wire at the alternator and ground it, ideally thru a fuse for safety
2) turn on the ignition... "BAT" light should come on
3) turn off the ignition... "BAT" light should go out
4) connect the blue wire, ideally thru a fuse for safety, to the positive terminal of the battery
5) turn on the ignition... "BAT" light should stay out

If you don't find any issues with the cluster or the wiring based on the above tests your alternator was probably permanently damaged when you hot-wired the excitation terminal directly to the battery.

If you fail 2, 3, or 5 the cluster or the wiring to the cluster has a problem.  To check the wiring you can pull the cluster and check for continuity between the alternator end of the blue wire and the cluster pinout... this site:

http://www.xjamiex.com/mk2resource/electrical/electrical.html

has the pinouts, depending on what cluster you have.... probably a CE2 given your model year.

If you have continuity then you're pretty much left with a cluster issue... looking for loose solder joints is the usual first step.



HTH,

Vince

[the caveman]

I had the same issue on a friend's Mk2 jetta a few years ago. She wasn't having problems, except the battery light stayed on. Car always started, no dim headlamps etc.
i checked the charging-was to spec- 13.xx volts, proper current with loads on/off. After a few hours of digging,I
then replaced the cluster, fuse box, X relay, and alternator and the light just refused to go out, except when not running, ignition off. She drove it like that for a few more months until it got stolen.

[vwjets]

Thank you for the replies.

Monsieur Caveman:

You're solution is the one I'm using right now, just to get around.

Vince:

I know I've seen you on another forum somewhere... I can't recall at the moment, but I'm sure you've helped me in the past.

I am going to follow your troubleshooting steps as soon as I can.

I should be able to figure this out now that you've pointed me in the right direction.

I'll report back with news of success or failure.

Thank you both for your replies!!

[vwjets]

Update:

I followed the five steps outlined by Vince and passed all of them.

1) disconnect the blue wire at the alternator and ground it, ideally thru a fuse for safety
2) turn on the ignition... "BAT" light should come on
3) turn off the ignition... "BAT" light should go out
4) connect the blue wire, ideally thru a fuse for safety, to the positive terminal of the battery
5) turn on the ignition... "BAT" light should stay out

I also noticed that the "BAT" light actually becomes dimmer when the engine is running.  One other thing I noticed is that the alternator belt wants to slip when the AC Compressor is engaged and the rad fan turns up to high speed (at idle).  It's not so much of an issue when driving, except between shifts.  I just try to keep the RPM from dropping to idle.


Additionally:  With the car running

1)  I checked the battery with the multimeter and measured 13.5-13.7 volts.

2)  I measured the big red wire at the alternator and it registered the same reading as at the battery.  (Grounding the multimeter both at the battery's -ve terminal and on the body).

3)  I measured the blue wire at the alternator and it registered a voltage of 6.7V.

I'm going to borrow a real multimeter from an electrician friend of mine to measure the amperage produced by the alternator and report back.

Based on the information provided by you all, I'm almost sure that the alternator is on its way out.  I remember it being purchased at Canadian Tire, but I don't have the receipt.  I guess I have to absorb that cost even though it is still under warranty.

[Soot Sandwich]

I remember researching this issue.  I believe it was Vince that had suggested it could be a ground issue.  My issue is a little different, when I am at spec idle my batt light flickers.  When I turn on the headlights the light goes out (or any sort of load AC defroster etc).  It sounds like your batt light wants to go out (as it dims when the car is on) I would invest some time cleaning up the grounds.  As a mechanical guy, if something weird is happening with electronics its probably a ground.

[the caveman]

I remember researching this issue.  I believe it was Vince that had suggested it could be a ground issue.  My issue is a little different, when I am at spec idle my batt light flickers.  When I turn on the headlights the light goes out (or any sort of load AC defroster etc).  It sounds like your batt light wants to go out (as it dims when the car is on) I would invest some time cleaning up the grounds.  As a mechanical guy, if something weird is happening with electronics its probably a ground.

Good point- see what happens when you provide a direct ground from the alternator housing and block or battery.

[bajacalal]

If you're getting +/- 6 volts from the blue (exciter) wire at the alternator, you have a MASSIVE voltage drop or short going on between there and the dash.

I would reckon you are getting enough electricity for the exciter circuit to function but the indicator isn't working as it requires alternator output voltage to exceed the battery voltage at the LED for it to go out.

This was all with the engine OFF, ignition ON, right?

[vwjets]

My measurements were with the engine running.

The only thing I need to actually measure is voltage from the exciter wire (disconnected from the alternator) with the ignition ON and the engine OFF.

But based on my troubleshooting earlier, I don't think there's anything wrong with the wire.

The battery is still being charged properly by my alternator, and my accessories seem to be working fine.  I'm guessing the alternator is supposed to give the blue wire 12V to turn off the light (but it isn't).

This is a moot point now that I've just received an "RMA" for my alternator and will be swapping it out.

If the light remains, then I'll have to live with it and NOT smoke out the new alternator .