72 Super Cheyenne light problem

[raws67]

About one month ago I bought an engine down by LA and was driving back from LA over the grapevine and I had no tail lights in the dark, not a place you want to be without lights. After scratching my head and calling a buddy with a wiring diagram I climbed underneath and followed the harness down the frame and there it was the round plug near the rear bumper I believe it was along the drivers side frame close to where they hang rear tires on newer trucks. The harness came loose just enough to still be hooked up but not make contact. If all your rear lights are out then that would be my best guess. Good luck