On my '88 735il, there is a gray/black wire coupled with a red/white wire in a two prong socket. (The original BMW radio had a yellow wire and a white wire connected to a male plug that plugged into this socket.) The red/white wire is the hot battery wire and the gray/black wire is the radio controls background lighting electrical source. I thought the gray/black wire was a ground so I doubled it to my other ground. This grounded out all of my instrument lighting. After I undid this and taped the gray/black wire off, lights work fine. Good luck.