Nancy calls me out to the tear the other morning as one of the tail light is on, and it is sitting there not connected to anything. Turned out to be moisture (it has been raining) had gotten into the seven prong plug and was shorting out. The holder for the plug puts the wire end up. A little contact cleaner and a plastic bag (to keep more rain out) until I can seal the end.
Love those "Electrical Gremlins"...sounds like you found it quickly though. I had a tilt bed car hauler once that started blowing tail and side marker fuses, I tilted the bed up to visually trace the wires, came up empty, replaced the fuse worked again, put the bed down and blew it again. I now knew what was happening but still took a keen eye and mirror to find the pinch point, pulled out the factory wire section and rerouted new wires clear of the pinch point thru a conduit I welded on and problem disappeared....frustrating as hell.
I fear the day that technology will surpass our human interaction, the world will have a generation of idiot's.