[Carl n Susan]

There definitely are two electrical systems. One is for the 120V system (ceiling fan, microwave, TV, Stereo, etc) and the other is for the the 12V system (lights, bathroom fan, heater, slide motors). The battery is charged via the 12V system.

You appear to have 120V working. But the 12V system is not. The converter is fed by the 120V system and produces 12V to charge the battery and run the other 12V devices. It sounds like the converter is not producing 12V as the battery is dead plus the lights don't work. There is enough output from the converter to run most of the 12V equipment (not the slides though).

I would start at the converter and make sure it is on and producing 12V out the backside. The are 12V reverse polarity fuses in the converter which blow if someone hooks up the batteries backwards. Has anyone played with the battery recently?

There is a 12V disconnect switch in the convenience center which disables 12V from the converter to battery and most 12V devices. But when connected to shore power the converter will power the lights and such (but not the battery).

Ensure the disconnect key is in the position where it can't be removed (that is ON and the normal position).