As I have recently have finished most of the roof repairs and other structural stuff My ? is the wiring to the 12 V system Black&white to the Batt I feel should be Blk Hot + batt and white Neutral - Batt
Reason is the ? is that heat nor the the fridge will fire Im thinking the polarity may wrong as I have read both units are Reverse polarity protected The furnace doesn't even try the thermostat checked good @ 7+ amps the blower would dim the lights the fridge pilot should at least have a pilot light (bulb) lit ??? I would try the 110 V but none available.
I forgot the owners Father in law lived in it until he got his own place as stated every thing was in working order