My first post, though I’ve read many threads. Thanks in advance. Bought our first camper a few months ago. When plugged in everything works. Nothing works from battery. Had tested. Wired correctly (thick white goes from negative to frame underneath). Found 3 fuses in good shape (replaced and checked anyway), 1 about 6 feet from battery (20 amp), 1 near converter? box (accessed from side panel, 10 amp) and one under sink going to furnace (7.5 amp). Not great with electrical but hoping to solve without taking in. When plugged in everything works whether “120V” switch is turned on or not which I thought was strange. Any things I can try? Thanks! I’ll attach a photo on next thread.