This is from the refer manual:
11. 12 VOLT DC CONNECTION This refrigerator model requires a 12 volt DC power source to operate the automatic energy system (even though it is designed to operate on 120 volts AC and gas). The DC lead connections are at terminals located at the rear of the refrigerator. (See FIG. 6). One lead is marked positive (+) and the other negative (–). Correct polarity must be observed when connecting to the DC supply.
Do not use the chassis or vehicle frame as one of the conductors. Connect two wires at the refrigerator and route to the DC supply.
It doesn't make sense that the refer would be getting it's 12v from the ignition system. It needs the 12v to run the control board whether it is running on gas or 120v. So if the ignition is off the refer is off.
Don't confuse this with the refer running the cooling system on 12v only. This refer doesn't have that capability according the manual.
So, I would just try running some jumper wires from the board's 12v inputs to the 12v house battery to see if that solves the problem.
Since this is not the original fridge, who knows how it was wired.
