It’s an ignition switched supply, sometimes owners use this for dashcams etc and add extra wires.It worked - it was very hard (stiff) to remove but I succeeded without damaging the trim. Thanks for your advice. One further query, I noticed that the ashtray/cigarette lighter plug at the back has 3 wires. I would have expected only 2 (12v DC positive and negative. What is the 3rd wire for?