ThetaTau87

For reference this is in my '89 GT that I just swapped a used '88 S4 5-speed engine into. I used the original 14-pin harness and alternator from my car after the engine swap. The alternator was charging normally before the swap. IIRC the volt meter read between 13-14v with the engine running, but the last time I drove it was Sept last year. I have yet to check the connections on the alternator to make sure I got them tight as this requires dropping the alternator to remove the rear cover for access.

The voltage warning light appears to be working as it should. When I turn on the key the voltage warning light is on. After starting the engine the light stays on for a moment then goes off.

Voltage on the gauge reads just below 12v with the ignition on, engine off. Slightly lower with the engine at idle. Increasing engine speed doesn't raise voltage.

If the alternator isn't charging shouldn't the voltage warning light come on? Or is that just when voltage drops below a certain level?

I tested the function of the light by unplugging the 14-pin connector and shorting the #1 pin on the vehicle side to ground and the light came on as it should.

On the engine side of the 14-pin there is 0v on pin 1 with the connector unplugged.

On the vehicle side of the 14-pin there is .026v with the ignition off and 12.24v with ignition on (12.41v at jump post.)

With the 14-pin connector plugged back in there is 1.40v on pin 1 with the ignition on.

Measured at the battery and jump post I get the following.

Ignition off (Interior lights on. All other accessories off)
Battery - 12.60v
Jump Post - 12.56v

Ignition on (Interior lights on. All other accessories off)
Battery - 12.40v
Jump Post - 12.32v

Engine running at idle (Interior lights on. All other accessories off)
Battery - 12.30v
Jump Post - 12.18v

Engine running at idle(All accessories on, lights, fans, AC, radio, etc...)
Battery - 11.87v
Jump Post - 11.40v

This seems like the alternator is not charging, but I can't figure out why the warning light isn't coming on.

ThetaTau87

Never mind. I'm an idiot and forgot to tighten the nuts on the connections.

AO

Hey Brad... make sure you don't forget to tighten the nuts on the connectors like an idiot...

< = = = = Says it all.

yorkee

Thanks for all the response. You think it is the regulator?

Alan

Yes - that's a regulator - but this time it seems it was loose connections..

Alan

James Bailey

And if the warning light is NOT working.........

PaulD_944S2

But that's not a healthy regulator.
The inner brush is worn down enough that it will soon be a problem.

dr bob

Often, that kind of brush wear means a similar amount of wear on the slip ring that it rubs against. You can sorth of see the slip rings with the regulator/brush holder removed, but it's from an angle that makes size judgement a little tough. Yes, that same angle... So it's really worthwhile splitting the alternator so you can see the slip rings on the back of the armature/rotor.