If you don't use a BMW GPS, the socket for that is, no doubt unused. Look at the wiring harness to the left of the headstock. You should be a able to find a lump that can be eased out of the cloth tape cover. This is an ignition controlled output so is great for something like an Autocom. It takes a special plug but I found that a bit of solder on about 5mm of the wire ends made pins that fitted into the socket quite well. Them just cover with tape.