f150 taillight problem

[Rocket Power]

I have no taillight on my 01 F150 SuperCrew.Brake light works fine, just no light when the headlights are on. I figured first it might be just a bulb, changed it and nothing. I just replaced the socket, since it's an easy change and I figured if they have a rack for them at autozone , they must have issues. Nothing. I get voltage to the socket, but it goes away as soon as I put in a bulb. I tried this same socket/bulb combo in the other side and it works fine.
Any ideas?
Could there be something jacked up in my trailer harness wiring that would do this?

[Irish]

I had the same problem in my jeep. Extend and bolt the ground wire some where else... it might be a bad ground.

OR

Buy a new tailight. My jeep had all three lights on the same circuit board. I changed the whole tailight and now it works fine!