The headlights and sun roof work sometimes and then they don't and then they do again and not at the same time,the lights work,sunroof doesn't and vise versa.The drivers side seat heater worked and then stopped working,the fuse is OK
Electrical problems on 1990 Audi 100
Early Audi/VWs had issues with their fuse panels causing intermittent problems with their electrical systems. The actual contacts go bad or the panel can get warped or corroded. So, you can check the fuse, and it is fine, but the circuit still won't work. This is one place I would look. Also, I think that this vintage Audi still uses the ceramic fuses,( blue, red and white) so they need to be replaced every 2-3 years because they look good, but no longer pass enough current to do the job. When I would 'service' the fuse panel, I would also clean all the contacts with electrical cleaner ( battery disconnected off course )and a soft metal brush to clean off all the corrosion. It is amazing how well a car runs and works after a fuse panel service.
Sounds like an intermittent fault to me Try getting the Sun roof to work when its Hot and the lights to work when its Dark. That way you can forget you have a fault. Hope this helps for further assistance I recommend an hammer for the sunroof and two candles and a retard to walk in front of you