emmarose007

Having trailer light problems with my 2008 F150 XLT. I believe the trailer wiring is all factory, but I am not 100% sure as I am the second owner. I have checked all the lights on my trailer and they seem to test out fine. I bought a tester for the truck lights and here is what it's saying: When the truck headlights are OFF, the left and right trailer tail lights work but the trailer running lights do not. When the truck headlights are turned ON, the left and right tail lights do Not work but the running lights do. I have checked the obvious fuses under the passenger side glove box and they seem fine. The wiring itself seems fine everywhere I can check. The connectors and connections seem fine. The grounding seems fine. I found a small black box with some fuses and such under the hood on the drivers side. There are two empty fuse spots in this box. I can't find anything about this box in my owners manual and when I called my local ford dealer they couldn't tell me what it was. Anyone else have a problem like this? I'm not sure how long this has been going on as we may not have noticed it until now (as the lights do "sort of" work!)