1977 Dodge Power Wagon Camper

Details of RV electrical systems can vary quite a bit. Somewhat typical is to have some sort of an isolator (either a high-current diode or a high-current continuous duty solenoid/relay) that connects the chassis 12V system and the house 12V system to let the engine alternator charge the hose battery while driving, along with a charger/converter connected to the house battery to charge it when plugged into shore power. Some older charger/converters had separate charger and converter outputs and various switching arrangements for connecting the 12V distribution (or various parts of it) to either the battery or the converter, sometimes automatically and sometimes manually. Newer ones just have everything connected together as it's become easier and less costly to build high-power somewhat regulated DC supplies.

I might guess the widow maker cord was used to connect the inverter (underneath the fridge in the pictures) to the rest of the 120V system in the RV by backfeeding an outlet. Trashing it and wiring things more properly is a very wise move.