Troubleshooting Brakes Lock Up and Stay Activated Until Trailer Is Unplugged From 2019 Ford F-150

Question:

I have a 2019 f150 with trailer tow package, [So it has built in factory brake controller]. The brakes a dump trailer are wired in with brake lights. All the light work great. BUT....when one tap the brakes they go to full brake lock up on the trailer ...and brakes on the trailer stay on even after letting off the brake in the truck. the only way to disengage the brakes is to unplug the 7 pin trailer plug Now with a factory brake controller this shouldnt happen , correct?? BTW, this is the way the trailer lights were wired from its factory, PJ 14foot dump, tandem axle, tandem brake. .the trailer has emergency brake box and is wired in with the brakes and lights of the trailer. ya know in the event that the trailer gets disconnected from the truck going down the road, the trailer brakes come on. To my knowledge this has never happened. never activated. So my question is.. can this emergency brake controller on the trailer short out and create the above symptom??

asked by: SmoketownMarty

Expert Reply:

That is correct, the brakes should not be locking up like that and you should not have to unplug them from the vehicle to disengage. The breakaway could cause this if there was a short or if it malfunctioned but that wouldn't explain why unplugging it from the tow vehicle disengages the brakes.

I would start by checking out the 7-way on your 2019 F-150. Make sure there is no corrosion that might allow power to jump from the 12V over to the brake output pin. You can also check to make sure it isn't damaged. After that, use a circuit tester # PTW2993 to check the brake output pin. If you have constant power on the vehicle side there is a short or the brake controller is malfunctioning. I would actually simulate the situation you described above so the brakes lock up and then test it just to be sure.

If it is on the trailer side it could be the trailer connector or a short. Take the tester and work your way back until you can identify where the constant power on the brake output circuit begins while still hooked up to the vehicle.

expert reply by: Robin H

Smoketownmarty

10/3/2024

I did disabled the power wire to the brakes which on the trailer...brake no longer fuctioned as expected. At least I have trailer lites. I will dig a bit deeper