Originally Posted by Peterrrr
It is more complex than that but it should not be. If you look at the build schematics for the battery compartment layout for your unit, then the wiring should be as shown by Mr.Turner. The potential problem or what is making it more complex is that normally extra cables are attached at the batteries instead of at the house terminal post ( where they should be attached). For instance they will connect the generator at the batteries . Again, according to the schematics, it should be at the house terminal post. I always add a catastrophic fuse at the batteries. In my opinion a Blue Sea battery terminal fuse block and fuse is a very inexpensive insurance against molten metal and exploding battery acid.
Ditto on battery fuses and Blue sea block. I use both on every vintage camper build. I ALWAYS take pics before taking stuff apart for situations like this, but in yours, I'd locate the main ground and go from there. Use a multi-meter set as in the pic, connect one end end to a known ground and listen for the sound. 4 wires should be easy (main ground to batteries, 2 foot long jumpers (1neg&1pos) to the other battery and the generator positive (which you should be able to trace its run). Whatever isn't a ground should be a positive, in theory, lol...