Whilst replacing the driver's side engine mount at the weekend (VX220), I noticed a wire hanging near the back of the alternator (nearest to the outside of the car) with a plug on the end. Coming out the back of the alternator was the corresponding plug socket.
They fit together so I plugged them in and the car still appears to be working.
What was that all about then? Couldn't have been that useful, was only a single piece of wire.