Hi guys.  This has probably been asked before but I’ve just managed to pick the wife up a bargain a3 s line on a 10 plate and had a pioneer da120 already in the garage.  I’ve bought the harness etc and it all works absolutely bob on but for some reason it won’t power off when the ignition is turned off.  Am I missing something? I’ve run the stereo power cable to the drivers side fuse box and used a fuse with breakout cable.  I’ve used what I assumed would be switchable fuses like the dash lights but this just stops the dash lights and the car won’t start.  I think it’s probably something simple but I can’t think of what.  Any help would be awesome thanks.

On some German cars the permanent live and ignition live are the wrong way around. If your head unit wiring harness has red and yellow wire you need to swap them round. Most have bullet connectors already so just swap them round. If they don’t have them then cut the red and yellow wire in the middle and fit bullet connectors to swap them that way.

I haven’t changed my head unit but as it’s German I’m convinced that this will be the problem. If that doesn’t work upload a photo and I’ll work it out for you.

The simple solution is to pick another fuse that is definitely switched from the ignition. That is exactly what I did when I added  a satnav some years ago, though I don't recall which fuse I used in the end. A test lamp or a volt meter will tell you all you need to know.