Unidentified R8 fitted to Audi R8 spyder

Has anyone fitted an R8 detector to an Audi r8 spyder? I want to mount it at the top of the windscreen near the rear view mirror (left side of mirror) and was wondering if there is a switched 12 volts up by the mirror? I have ordered an owners manual for the car, so should know soon, but thought I would ask here in case any of you have already fitted a detector to the same car?

thanks Gary