Test eldorado pcm

I have a 96 Eldorado. Can anyone tell me how to test the Pcm & BCM? I found that there is a battery drain somewhere related to the raido, thats killing my battery. I spoke to a Tech. person that repairs Cadillac radio’s and told him, when I unplug the radio the drain is gone. He said it’s possible the radio is causing the problem, but his experance is, that it’s probably the PCM or BCM. He asked if the clock display goes off when I shut the ignition. I told him it does, so that elimates that possibility. There is one other thing he said, there may be an accessary relay thats not part of the radio circuitry. He does not know if there is one for or where it might be. So, it seems to go back to the PCM or the BCM. I have 3 questions. Is there such a relay, if so where is it and how do I check the PCM and the BCM? I’ve ben tracking this drain for two months and I’M almost there. I would be overjoyed if I can beat this thing.