On my '63, all of the trailers 12v
was one big circuit of 10 gauge blue wire, spliced inside the walls or where ever was easy. There were 2 auto reset circuit breakers, one at the battery and another in the umbilical charge line, just inside the front wall. The wire routing was drawn on the inner side of the exterior shell with grease pencil.
Exterior lights were wired typical of any utility trailer with the wires routed down the street side, spliced and sent to the approprate lamp as needed.
The 110V was only marginally better because it at least included a breaker box. splices were sill inside the walls.
My trailer had a schematic in the closet attached to a wall but it truly was a waste of paper. There is no way that the diagram would be useful for trouble shooting any issue, I'm convinced that the sole purpose was to meet Code by displaying it.