T25 1.6TD Generator warning light on

[simonruth]

The generator/battery warning light came on this morning and now remains on. All belts present and tension seems ok. Fiddled with alternator connections and all seems ok there too. is there anything else I should do/worry about?! Cheers.

[Ralf85]

Worn out brushes on the voltage regulator pack? Cheap easy fix if it's that.

[kevtherev]

yes ..you need to change the regulator/rectifier brushes

[simonruth]

Wow - that was quick! Will try that next. Thanks.

[Ralf85]

Takes me about 10 mins to change one. Just two screws to undo. These packs are available everywhere. Don't continue to drive far before replacing it as you will flatten your battery.

[Oldiebut goodie]

Not such a worry on a diesel - only a solenoid to hold open + turn signals/brake lights. You can run for ages on a charge.

[ZsZ]

Did you measured the voltage at the alternator outputs?
As mentioned above, check the regulator for worn brushes, and also check the D+ connection (blue wire) beside the battery and in the black box. Broken wire in that circuit can cause similar symptoms.

[simonruth]

Haven't done that. If its not too stupid a question, where do I attatch the multimeter to the alternator!!(I'm ashamed of my ignorance!) Also blue wire looks ok as far as I can see, but can't locate it in the black box! Connection to alternator and spade connector by battery seem fine. Thanks for the advice.

[ZsZ]

Do you have an alternator with screw on connectors (one big M8 and one small M6 threaded bolt) or with blade connectors (the loom has one square plug with two big and one small blade connector in it)?
The big connectors are the voltage output (B+), the small connectors are the warning light output/feedback current/ (D+)

If you have the screw on type, then it is simple: the voltmeters positive (usually red) wire goes to the screw, the negative (usually black) wire goes to the ground (body or battery)
On the blade type it is a bit tricky, you have to open the plastic plug carefully to reach the connectors.

How the circuit works described here at the bottom:http://www.vw-resource.com/alternator_wiring.html

[simonruth]

Just got the multimeter out. Battery is at 12.5 V with engine off, dropping to 12.25 V with engine running. 5.3 V from blue wire (bolt) on alternator with engine running,0.8V from red (which is a spade connector) Does this make any sense?!

[simonruth]

Also have leisure battery which receives charge via the alternator - that is at 12.4 V.

[kevtherev]

you need a new brush pack.
The figures prove it

[simonruth]

Thanks for the advice. Ordered the part from JK. Fingers crossed!

[simonruth]

Replaced voltage regulator - no joy! Turned out to be a knackered rotor arm! Thanks for the advice though - I've learned a lot.

[California Dreamin]

Sure it wasn't a loose bumper end cap.....

Martin