House batteries not charging from chassis (SOLVED)

Success! I found a switched lead in the uplift wiring (ambulance, RV, etc) cavity behind the drivers seat; it was right next to the orange that had been snipped from the connector. Odd that I never found a fuse for it....

All has been buttoned up and is in working order. I learned a lot, and hope that it will help others with a Precision Circuits BCC/BIM. There's a lot going on in that box, but with a little understanding of the theory of operation, it's much easier to troubleshoot & fix.

Thanks everyone!