Troubleshooting Trailer Bake and Turn Signals Not Working on Trailer Towed by 2003 Ford F-250

Question:

I got no brake lights or turn signal light when hooked up to my rv. Truck is 2003 F250 with one bulb turn/ brake light. I had the rv checked with no indicated problems. RV checked good. I changed the brake controller I have brakes with the manual slider and while pressing on truck peddle. I have running lights no turn/brake lights. I have never had this problem before. I upgraded the controller after I found the no lights problem. DO I need a pulse preventer. How do I get my lights back?

asked by: rus s

Expert Reply:

A pulse preventer would be needed if when towing with the hazards on, the display on the brake controller also flashes. This could then potentially be felt in the trailer brakes if the brake controller is set to a high level. It would not help with the turn signal and brake light problem.

In situations like this, it's best to start with the easiest possible solutions. First, I recommend cleaning the connectors on both the truck and the trailer. Any dirt or corrosion could cause a problem. Next, check to make sure the grounds on the connectors are attached, not loose, and not corroded or dirty. If your tow vehicle has relays or fuses used to activate parts of the wiring harness, check those to see if any need to be replaced.

You can also check to make sure the functions at the tow vehicle side connector are functioning properly without the trailer attached. Use a circuit tester like # PTW2993 to make sure the functions are correct. If they are not, there is a problem somewhere in the tow vehicle wiring. You will need to check for loose or broken wires the length of the wiring. If they are working properly, something is wrong on the trailer side wiring.

With the trailer connected, test for functions again behind the trailer side connector. If the functions are correct, keep checking the wiring all the way back.

expert reply by: Michael H