What does this wire do ?

I replied to your questions in your original thread. It kind of seems that you're jumping around quite a bit through the electrical system. May I suggest we take a step back and work on one issue at a time. Other wise it gets confusing for everyone. I know your daughter is probably impatient to use her new car but sometimes what seems like the slow way through is realty the quickest way through a problem and its becoming apparent this car has multiple electrical issues.