I drive a 1992 200tdi 90. My battery light has started coming on and flickering very dimly when I'm driving. It gets a bit brighter at low revs, but still flickers on and off. It goes out eventually but will come on again after a while.

I've done a search on here but it didn't come up with anything relevant. Any ideas?

Checked your fan belt?
Could be the brushes are on their way out.
Clean all terminals and make sure they are tight.

alternator

alternator belt slipping? probly alternator tho.

mine does exactly the same thing, although it does disappear at higher revs. I need to sort it out. I found that the two bolts on the bottom weren't at all tight the other day, so tightened them up, and also tightened the fan belt a little as well. Pretty sure it isn't slipping, but still got the problem. Would anyone say that changing the brushes was an easy job on an alternator?

If it's a standard alternator, the brushes are part of the voltage regulator assembly which bolts on the back. It is possible to remove the regulator in-vehicle, but a lot easier to remove the alternator first!

Having removed and replaced mine once (in-vehicle) I wasn't convinced that the small-headed bolts would cope with a repeat of the procedure. Instead I bought and fitted a new, higher-rated alternator. Once removed I could see the severe corrosion on the main connections (which are NOT part of the regulator) -- probably due to the muddy wading that a previous owner did -- and I think complete replacement was the right move. But then, it was 16 years old!