For assorted reasons your photos
1: did not display properly (Too wide)
2: I'm not good working with photos.
You mentioned extensive experience with house wiring. I'm cross trained. I've done house wiring but I'm a certified electronics technician.
In house wiring WHITE is neutral. Black is hot (at least usually)
In automotive and electroic wiring Black is "Ground" Usually (not always)
IN RV.. Well the HOUSE is wired by (usually) electricians (House standard) and the chassis on a motor home by Automotive types.
So your multi-meter is your friend when working on the 12 volt sides of life. Check polarities.
