Sounds like he doesn't want to run the current for the trailer lights through the wiring in the truck?
Having the 4 wires to the trailer triggering their own relays would work. Though it would be overkill, unless he has a few kw of lights.
I have a small fuse block inline with the wiring to the trailer. If a wire on the trailer shorts out, it will hopefully blow that fuse, keeping the lights on the truck functional.
Thank you too for the input, I am not one to rely on "hopefully" although a standalone fuse panel was considered.
