Troubleshooting Electric Trailer Brakes and Running Lights not Working on Trailer, 2006 Ford F-150

Expert Reply:

I have a couple of ideas that may help solve the problem you are having on the 2006 Ford F-150. First, you mentioned that the truck has the tow package. It is possible that you will need to add or replace fuses and/or relays to allow the tow package to be fully functional. Your vehicle owners manual should have the locations of these fuses/relays and you can check to make sure everything is present and in working order.

Next, you can check some of the wiring to determine if it is the culprit. You will need a circuit tester like the Quickee # 3808 if you do not already have one. First, sever the blue wire coming from the back of the brake controller making sure to leave enough wire to splice it back together.

With the wire severed, test the wire while using the manual override. If you get a signal then you know the brake controller is working and the trouble is somewhere else. .

If there is no signal with the brake pedal or the override, then something is wrong with the brake controller and it will need to be replaced. If everything is working properly, reconnect the blue wire and move on to testing the trailer connector.

While someone in the truck presses the brake and uses the manual override, test the pin in the 5 oclock position (if looking at the face of the connector). If the signal comes through, you know the problem with the brakes is not on the truck side. If there is no signal, you know there is a break in the wiring somewhere between the controller and the connector.

The running lights could also be affected by missing tow package fuses/relays. If they still do not work after changing or adding the appropriate fuses/relays, you can go back to the trailer connector and do some testing with the circuit tester. Test the pin in the 11 oclock position (with the truck lights turned on). If no signal is getting through, you know there is a problem along the wiring harness somewhere that will need to be repaired.

You will also want to check and make sure the ground connection is good. Many wiring problems are caused by a bad or insufficient ground. Additional problems could also be caused by dirty or corroded connections. Examine the front and back sides of the vehicle and trailer side connectors for any dirt or corrosion and clean it out.

If everything on the truck checks out then you know the problem is on the trailer side. Again, check the ground coming from the trailer side connector. Make sure it is attached to a clean and corrosion free bare metal surface. You will also want to make sure the trailer connector is pinned out to match the truck side connector. I have included a link to our wiring FAQ that shows the standard configuration.

For the brakes, you can listen for them to engage when someone steps on the truck brake with the trailer connected. If everything else is working properly yet the brakes do not engage then you know something is wrong with the brakes. It could be the ground wire or brake signal wire is not properly attached. I have included a link to an FAQ on testing brake magnets for you.

For the running lights, usually trailer tail lights ground through the mounting studs unless they have a ground wire. In either case, check to make sure the grounds are connected to a clean and corrosion free bare metal surface.

expert reply by: Michael H