[dmjlambert]

I had a license plate light that did that same thing. I took the socket off the truck, cleaned it up really well, cleaned up the hole in the bumper, tested it off the truck and it worked fine. No matter what I did, it did not work when inserted all the way onto the truck. In my case the only thing to do was replace the socket assembly, and then it worked fine. I am pretty confident at fixing electric stuff, but that bulb assembly was mysterious.