Tailgate lock and right tail light don't work after unplugging trailer

[TogaLock77]

I have a 2019 Tradesman. No previous problems and I recently pulled my trailer with no issues. Today, without the trailer attached, my tailgate would not unlock and I received the message that my right tail light was not working. I checked fuses and wire connections and couldn't find any issues. Later in the day, I took the trailer to pick up mulch and used temporary magnetic mount trailer lights. The trailer lights functioned normally, yet the right rear light on the truck still didn't work, nor did the tailgate lock. When we got back from the mulch pickup, UPS had delivered my new trailer lights. I hooked those up and the right rear light on the truck along with the tailgate lock started working. Unplug the trailer lights and they don't work.

I assume I have a grounding issue somewhere, but I'm not sure. How did everything work normally and now only works with the trailer. Any suggestions?