Hi there MisterP,
I have a 1975 P6b with a blaupunkt radio fitted (with matching speakers too).
I'm having trouble removing it tho.... it doesn't go! The fuse looked okay, I've also noticed the clock doesn't go, I wonder if they use the same line. I'll be taking the dash apart one weekend just to have a good look back there and see if I can get a bit more power out of the heater system.