I have a '99 A6 Avant the third brake light and rear windshield wiper work intermediately. According to my haynes manual(passat/A4)these share a ground at the trunk lid/rear left pillar. Can anyone tell me where this ground is at. I'm thinking the ground is the most likely problem, also my rear sub/amp cuts out or gets scatchy occasionaly, is this the same ground location, or a completely different problem? Any help greatly appreciated.