Troubleshooting Brakes Activate When Featherlight Horse Trailer Plugs Into Ford F-350

Question:

When I plug my Featherlight horse trailer to my f350 the trailer disconnected light comes on ,Also the trailer brakes lock down. Also if left plugged up over night it will run the truck batteries down. Help!!!

asked by: Butch

Expert Reply:

Hi Butch; since your brakes lock down I'm guessing you have damage/corrosion on the vehicle or trailer connector. This would allow the power to jump from the 12V over to the brakes and activate them. I'm sure that would also cause your problem with the trailer disconnect light and the drain on the battery.

Go ahead and visually inspect them to see if damage/corrosion is present. If the vehicle side has corrosion you can try cleaning it or replace it with the # HM40975 which fits the 1999-2024 F-350. If you find the same on the trailer side you could swap the connector with # PK12706 if cleaning doesn't work.

If you don't find anything with the connectors I would start testing for power with a circuit tester like # PTW2993. Go ahead and test behind the connector on your truck. If you have 12V power on the brake output wire go ahead and jump back to the brake controller and test. If you still have 12V power it is a problem with the brake controller which will likely need to be replaced with one like the # 90195.

If you don't have power on the brake output at the brake controller you must have a short in the wiring somewhere which you will have to locate and repair. If it is on the trailer side I would also be looking for a short in the wiring.