1972 GMC Rear Wire Harness C30

[jlampka]

While under my truck, I noticed a hanging 4 wire connector (circled in photo) and mounted gold anodized cylinder with a red wire hanging from it (also circled in 2nd photo). Both are near the rear bumper and I am not sure what both are for. I have the camper wiring option if that helps any. Any help appreciated.

[Redneck Rydes]

Could possibly be for a extra long slide in camper,where the tail lights were on the camper,so maybe a extension harness was on the camper to run the lights.The red cylender dooey,looks like a old style resister for something possibly on the slide in unit.