Audi20v.net

Simple Check for it is the following

1. Remove footwell cover (driver's side ... this is actually the whole shelf).
2. Remove ABS relay (should be middle row all the way to left and it has a red fuse in it which is 10 amp I believe).
3. Look at fuse ... is it blown? If so, then here is your problem. Don't bother replacing fuse ... it will blow again. Replace the relay. If you still don't believe me, go ahead and put in another fuse and I bet it too will blow. This will prove the relay is toast.

The relay is found on all the 1990 - 1992 audi 90's and coupes ... regardless of drivetrain. Best way to make sure is to look at the part number on relay.
What happens is that there is this mother-of-a-diode inside that I can only assume shorts out over time. This diode is put there to 'absorb', if you will, any counter-EMF that occurs from turning off the ABS pump, so that the rest of the car's electronics doesn't go berserk.