Trailer Lights Not Working when Headlights are Turned On On a 2013 Ford Edge

Question:

I have a 2013 Ford Edge. When I hook up my boat trailer all the lights work fine. However when the headlights go on all the trailer lights stop working, with the exception of the running lights. I have checked all grounds and all connections and everything is good. I was told by a mechanic that there is not enough amps getting back to the trailer lights when the headlights are on and that I would need to have the vehicle rewired. Is this accurate? The vehicle was wired from the Ford factory with what seems to be a standard harness.

asked by: Mike R

Expert Reply:

There is one sure way to determine if the factory trailer wiring harness on your 2013 Ford Edge is pushing back enough power. You will need a multimeter such as # PT89ZR. Have someone sit in the vehicle and go through the light functions while testing for amperage.

You would also need to determine how many amps each light draws. Then with some simple math you can figure out if the trailer is drawing too much power to power the lights when the running lights are on.

An easier way to do this would be to disconnect some of the lights. If everything then starts working (except for the disconnected lights) then the trailer lights are likely drawing more power than what the factory wiring harness is capable of. If the disconnected lights somehow start working then your trailer is haunted and you should sell it.

You can replace the lights on the trailer with LED lights which draw much less power.

It could still be a poor 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.