So no idea what that wire was for, definitely nothing to do with sat nav or radio system, can only assume it's from something that the first owner had fitted, maybe a Bluetooth phone system. Anyway, the CD player still doesn't want to work, won't even let me load a CD, but at least I managed to get all the cd's out of it. Couldn't see anything wrong inside it , so guess fault is on one of the circuit boards 🤔