Trailer Running Lights Do Not Work When Connected to a 2011 Ford F-150

Question:

Connecting new trailer using round seven/flat five adapter to 2011 F150. Turn signals and brake lights work but have no side marker or taillights.

asked by: Chris S

Expert Reply:

First, check to see if the running light circuit on the 7-Way on your 2011 Ford F-150 has power using a circuit tester such as # PTW2992. If it does not then there is likely a fuse blown or blown or missing relay. Use the owners manual to locate any fuses/relays related to the tow package wiring.

If there is power on the truck side connector then plug in the adapter and make sure there is power on the outside of it. If there is not then the issue is with the adapter.

If there is power at the truck 7-Way and when the adapter is plugged in then that indicates a problem on the trailer side. It is likely a bad ground.

Ground problems normally show up when there is more draw on a system such as when you have the running lights on and then use another function like a turn signal or brake light.

Make sure that the vehicle side and trailer side connectors are clean and free of corrosion inside and out. The main connector grounds should be attached to clean and corrosion free bare metal surfaces.

The light grounds should also be attached to clean and corrosion free bare metal surfaces. If there is anything between a light ground and the metal trailer frame or if the trailer has an aluminum frame, tilt bed, or folding tongue, any of these things can interrupt the ground. Running jumper wires from the light grounds to the main trailer connector ground can help.

expert reply by: Michael H