Could just be a broken wire somewhere in the truck. Had this happen back when I owned a pick up. One of the wires to the harness just went bad causing all kinds of trailer light troubles. PITA to find the guilty wire and fix.
Sure as snow is white, I make a comment on trailer lights and immediately posting, I have my first issue in 10 years. LED tail lights and no left turn signal not brake light. With the old incans I would suspect needing a new bulb. Not so with LED's. Fun begins this weekend to track this one down
Fuses? some newer vehicles have fuses in the back near the taillights. I had an issue at U-Haul I could not rent a trailer because not all the lights worked, ended up been a blown mini blade fuse near one of my tail lights!
Not fuses.. they are all good.. I think it is the IPM. Tonight I hooked that Camper and Scaup up at the same time... Both worked!!! Hope they do tomorrow night!