Well, I am in the middle of a shell off restoration of a 1960
Tradewind. Part of that is to replace ALL the wiring with new which I am in the middle of right now. I found it interesting that originally, every bulb (running lights, taillights, turn signals, license plate light,) had a dedicated wire leading from the pigtail to it. There was no daisy chaining--every bulb on a single wire. I think there was 11 separate wires in all.
Assuming your 2 year younger trailer was wired in the same way, you would have to assume your problem lies somewhere in the pigtail or connector to the tow vehicle. It would be impossible for every single one of those wires to fail at once since you said everything went out at once.
Hope this information is useful to you in some way.