To me it looks like the original AC/DC switch has been replaced with a toggle switch/plate........just doesn't look OEM.
Couple of issues.
With mode selector switch in 'gas' no electric heating AC or DC should occur
With mode selector switch in 'electric' AC heating (with shore power) should occur when AC/DC switch is UP. DC heating (from battery power) should occur when AC/DC switch is DOWN.
With mode selector switch in 'OFF' nothing should heat (gas, AC or DC)
I would remove AC/DC switch with plate........pull complete plate out with switch......and check which contacts have AC voltage and which have DC voltage.
And check that NO voltage flows thru switch when mode selector switch is OFF or on GAS
One other thing........those models of compact fridges built between 1987 and 1995 had a recall on the gas valve. Recall involved replacement of gas valve.
LINKModel Serial number range
874EG2 01000-03988
874EG3 01000-02347
875EG2 01000-24711
875EG3 01000-05696