Hello, I just purchased my first audi, a 1990 audi 90 for 1500$. It runs great, but the overheating light comes on. Sometimes when I've been driving it for awhile, but the other day it came on as soon as I started the car. Also, there's this electronic clicking sound that is coming from the dashboard, it sounds like a relay going off, it also happens intermittently. The overheat light comes on every time I drive the car, just at different amounts of driving. I topped off the coolant and it isn't leaking any. ANy ideas about what this might be and how much it may cost to fix?? Is it really overheating and how can I tell?
I'm not very mechanically inclined so sorry for the multitude of questions!~

First, the electrical system in older Audi's can be problematic. I would check the thermo switch, it is a separate unit from the temperature gauge sender. You could have a problem with the contacts, either corroded or broken as well as a defective switch. The relays, several possibilities, defroster, AC, and heated seats will cycle the relays but there are other possibilities. You will need to find out which relay is clicking.