Regarding the lights steaming up, make sure they're fitted correctly and are 100% sealed and there's no hole or crack anywhere.
By light you mean error, right? If so, what does it say on the MFD screen? If you have the smaller screen which doesn't say what the error is, then I suggest using a VAG-COM cable or visiting a local garage that has it in order to identify the error. Go around the car and make sure all the lights are working correctly, I am sure one of them is out which is why you're getting the light error.