Audi Repair: Temp light, temperature gauge, warning light

Question
My temp light comes on out the blue, sometimes it comes on when the air is on, is this a radiator problem or thermostat or something real major.

Answer
Sounds like perhaps a faulty warning light switch.  Does your temperature gauge show anything strange?  The temp warning light switch is in the cylinder head; I would check the wires going to it for chafing or a short, and also check if the switch itself is malfunctioning.  Make sure the water level is OK and that you do not have any air in the system.  Let me know what you find,  Jan