So I installed a after market radio. Apparently BMW doesn't have a ACC+ wire, only a constant 12V (yes it was weird for me also) I checked all the cables with my multi meter but there wasn't a single ignition 12v So I connected a cable straight from the fuse box where I found a 12V ignition socket. Hooked it up to the radio and it worked, radio turns on and of with ignition. BUT THE PROBLEM IS, my radio won't remember anything, for more or less 15 minutes without the key ignition it does remember everything but if I leave the car without ignition for a hour or so it lost everything, the original BMW radio didn't had this isue at all. So does anybody know what is the problem and how I can solve this ?
Most cars, including BMW, have a key controlled ACC supply - usually position 1 on the key, with position 2 being the ignition (battery warning lights etc) and position 3 being start - (some older diesel vehicles had position 3 as engine heaters, with position 4 as start.
Find the wires connecting to the ignition switch - under the steering column and check there with your multimeter.