One problem related to headlight switch has been reported for the 1999 Audi Quattro. The most recently reported issues are listed below.
I have a 1999 Audi a4 quatro. I've owned the car for just over 3 years and have had to replace the headlight switch 5 times. The switch is poorly designed. Electrical heat melts a plastic part in the switch causing it to fail and the headlights to stop working. This is a danger due to the potential of fire and also the loss of lighting while driving. I have researched this on the web and I am not the only Audi owner with this issue.