Ok, not sure if anyone will see this but update is that there was no fuse, the red wire is positive, and it wasn't grounded- that little black wire goes to a small box attached to the frame right there. No idea what it's for. I would post a pic but it's irrelevant because there's no way I can use this system as is. I found a burned wire in the mass of wires inside the small panel cut-out where the battery leads enter the underside of the trailer.
New question- how crazy would it be to run temporary wires from the battery to the water pump fuse in my fuse box? And how exactly would I do that? I can't afford to pay for rewiring and don't trust myself to do it. The water pump is all I really need battery power for right now since I have lights hooked up to city power.
