How can I determine the cause of a electrical problem. My original radio need code resetting each time I turn the engine off. Why is that?
I think it because your original radio had an anti-theft system requiring that code. The radio is now 32 years old. The capacitor or small battery that provided the tiny amount of power to remember that code when the ignition is turned off has died. I suggest searching for vintage BMW parts specialists may identify a vendor who can repair the radio.
Check fuse # 21 in the power distribution center, that is for the radio memory power.