There is one 120v breaker box, and a set of 12v
fuses located elsewhere. Originally I think the fuses were inside the Univolt, but sometime in the late 70s/early 80s they put a 12v
fuse block on the front wall below the windows/behind the couch at least on some trailers.
I don't think you have a 12v
problem, from the sound of things. Do your lights work (at least for now)? It would be good for you to find out if you have 120v power to the 12v converter/charger if you're having problems with the 120v system.