Two thing on the raod side of the trailer that pass a lot of owners initially. The fiber optic taillight assembly. This allows light check if driving alone - brakes, blinkers and running lights. Pretty neat idea and works great if clean and aligned.
There is also a small, facetted button further to the rear on the roadside of my 73 Excella. This is a polarity check. It is useful when hooking up to city power with only two prongs. If the light is on, reverse the plug. It may flash once in a while and that is not a sign of reverse polarity. Also, a neat idea. My 71 landyacht di not have that feature.