Trailer Brakes Work Fine when Testing Parked but Brake Controller Work Intermittently when Moving

Updated 07/21/2014 | Published 07/19/2014

Question:

I am having some problems with my trailer breaks. I have taken this truck with the trailer to 2 trailer experts that have not been able to fix the problem and just keep throwing things at me like a break controller I dont need, A break away batter I did not need etc.. Here is whats happening When the breaks are applied in my yard and I lift up the trailer on one side you hear the hummmmmm of the breaks and if you try to spin them by hand they do not spin and the break controller reads between 12-14 on the dispaly. Each side seems to work and hummmm when applied in the yard.. Then when on the road different story all together.. When pressing on the breaks sometimes I get the break controller to go up to 12 then with the break still pressed goes down to between 4-6. during this time NO BREAKS are felt being applied. sometimes when you hit a bump the #s will jump around BUT still no breaks feeling engaging. I have climbed under the trailer wiggled the wires took a rubber mallett and hammered all over the place to simulate a bump etc. with no results. I have gone as far as to run a whole extra ground from the trailer to the truck with no result. The truck is a 1999 Ford F350 dually with 7.3 engine. Break controller is a PILOT break controller. Please help me I am at a loss and have spent $$$$$$ dam near a thousand... Thank you in advance for the help..

asked by: John

Expert Reply:

I think you are on the right track with the ground. When there is intermittent function like this it is almost always a ground issue. When traveling there is a certain degree of bending and flexing on the trailer that would be difficult to simulate at home.

There are some tests you can perform at home to determine where the issue is. And you should not have to spend any money to perform these tests. In the truck cab you will need to sever the blue wire several inches from the back of the controller. Then use a circuit tester such as # PTW2993 to test the end of the blue wire coming out of the controller. It should only have power when you apply the manual override or brake pedal. If it shows power at idle, then there is something wrong with the controller and it will need to be replaced.

If it tests fine, then reconnect the blue wire. Then move on to the truck side trailer connector. Many times, dirt or corrosion can cause a short or poor connection in a trailer connector. Make sure the truck and the trailer side connectors are clean and free of corrosion inside and out.

You can test the brake output pin and it should only show power with the manual override. If it shows power any other time, then there is a short somewhere between the connector and the brake controller you will need to track down.

If the truck side checks out fine, then it could be the wiring to the brake magnets or the magnets themselves. Inspect the power wires to the magnets and look for pinched, frayed, or damaged wires and fix as needed. Make sure the ground wires are attached to clean and corrosion free bare metal surfaces.

You can visually inspect the magnets and if you can see the copper windings coming through the magnets will need to be replaced. To further test the magnets, you can follow the help article I have linked. I have also included some help articles on testing and troubleshooting brake controllers for you.

expert reply by: Michael H