I'm leaving this forum and have deleted all my work in this thread.

 

I think the BCU pulls some power thru there, which would be normal. But how much power would be the question. You'ld need a meter with amp scale. You'ld expect any drain for clock, CPU, BCU, radio memory - to be pretty low, way less than an amp. Don't know about your test light, but a regular tail light bulb will glow bright on a heavy drain, and not so much on low current drain.