How do you tell if your 1998 Audi A4's switch is bad or if it is just a relay?

best way to test a relay is remove it from board, get a 9v square battery and touch the switching terminals on the relay, the relay should click if its working. You can then test resistance through the relay. You can also check the feed to the relay, if theres pwer to the switching terminals on the relay, chances are the switch it ok. If no voltage, switch or wiring.