Have a Texas diamond plate rear bumper , license plate lite went out 1 wire the socket uses bumper as ground, it was out replaced with same unit, crimped connections , scraped hole in bumber to make good ground, and Nothing, heres the twist went to my tailgate marker bar (3 red Lights) cut the positive and spliced the license plate lite, still nothing, now the bad part put the wires back together for my tailgate bar and they are out, checked all fuses and checked tailgate lites with a fender Dually marker lite and it is good.

 

Using a pointed end test light, attach the ground clamp of the test light to the disconnected wire that normally goes to the 3 bar marker. (We KNOW there is power in it as the fender marker light lit when you put that wire to it) Now, with the clamp end of the test light clamped to the good wire with power in it, touch the pointy end of the test light to various points of the body, bumper and tailgate. If it doesn't light the light, you lost the ground to whatever you're touching with that pointy end. If it lights, start checking the ground connection in the 3 bar marker in the same manner, using that pointy end. Somewhere, you're losing the ground by the sounds of it.

Hope this helps!

chaikwa.

 

The license plate lights were out on my truck and the wires were melted into. The wires were fine at the lights. I started at the light going up the wires and both were melted at the first factory wiring plug. The plugs are right behind the bumper on the frame rails.

Hope this helps,
Rodney