Troubleshooting Trailer Running Lights That Dont Work When the Rest of the Lights Do

Question:

I have a 2011 ford f150 and a little landscaping trailer. The break and signal lights work perfectly, but the running lights on the trailer dont. All the lights on the truck work perfect also. There are two marker lights on each side and they dont work either. I have clipped and regrind the ground on the trailer so its a nice clean connection and I had also replaced every fuse in the truck that the manual called for TT. Then I started to dig into the wiring on the trailer and found a few wires worn down and corrode. I replaced all bad wires and I still have the same issue. Any help would be appreciated. Thank you!

asked by: Anthony

Expert Reply:

In addition to the main ground, each taillight assembly at the back of the trailer must also have a ground. These are most commonly grounded to the trailer frame or through the bolts of the tail lamp assembly. I recommend checking to make sure that each light on the trailer has an adequate ground.

Next, I would check to make sure that both connectors, vehicle and trailer, are free of dirt and corrosion. If both are in good condition, I would move on to testing the vehicle connector. Test each pin, using a circuit tester like # PTW2993, to make sure that it has power when each light or signal is activated. If any of these are not functioning properly there is most likely something wrong with the connector on the truck. If all pins function as they should, the issue is somewhere on the trailer. In this case I recommend inspecting the wiring on the trailer a second time just to make sure there aren't any wires that are exposed or damaged.

expert reply by: Leah S