I recently bought a used 1994 BMW 318i. Something is draining the battery. I've replaced the battery and the alternator. Key out engine off drain is still present. Radio displays CODE. What is draining the battery?

Iwould pull the negative battery cable and put one end of a test light on the cable and then start pulling fuses (one at a time), put other end (probe) of test light in the fuse hole and see if any of these fuse holes cause the light to illuminate, if so, that is your problem.