Brake and Turn Signal Lights do Not Work on Boat Trailer

Question:

I just bought a boat and trailer. Hooked up to my 7 pin adapter 4 pins used and found I had no right turn or brake light or 4 way flasher on the right side. Cleaned all the grounds and no change. Bought a complete new light package with new 4 pin harness. Installed and no change. Neighbor came over and hooked up with his truck. All worked!! Checked the fuses in my truck. seems like all are fine. I have a 2007 ford f150. Tested the pins on both the 4 and 7 setup that my truck has and they all blink or stay continuous depending on hitting the brakes or using the signals. Im lost!

asked by: Ken

Expert Reply:

Since the trailer lights are working with a different vehicle, that would indicate an issue on the truck side. But it could also indicate a problem with the adapter as well. You will want to check to make sure the adapter is pinned out correctly to match the way the trailer and truck are configured.

Make sure the trailer connector on the truck is clean and free of corrosion. On a 7-Way corrosion can also build up behind the connectors where the wires attach.

Check the owners manual for the locations of all of the fuses and relays related to the tow package wiring and check them. It could be a bad relay on the right side. If you find a relay, you can try switching the left and right relays and see if the problem jumps to the left side. Even if you get some power at the trailer connector, if a relay is bad or missing you still may get some power but when a load is applied to it, it will not work.

Double check that all of the grounds, from the main ground, to each light, is attached to clean and corrosion free bare metal surfaces.

expert reply by: Michael H