Troubleshooting Brake Controller Not Working When Brakes Are Applied but Works With Override Switch
Updated 03/15/2025 | Published 04/21/2010
Question:
My trailer brakes will not work when appying the truck brakes but will work when you push the test button on the controller box! Does this mean my box is bad or what?
asked by: Sarah
Expert Reply:
This sounds like the trailer brakes are not receiving the signal from the brake controller when you apply the brakes. I believe what is happening is that you may have a loose, broken, or inaccurate connection on the red wire from the brake controller.
The red wire needs to attach to the stop light switch above the brake pedal. It connects to the wire on this switch that carries a signal ONLY when the brake pedal is pressed. It should not have a signal at any other time. Use a circuit tester, like # PTW2993, to test the wires. If your brake controller red wire is not connected to the correct wire, or is loose or broken, this would cause the problem you are experiencing.
When you use the manual override, it bypasses the need for a brake signal on the vehicle and applies power to the trailer brakes. That is why it works when you hit that button.
If you find that the red wire is connected in the right place and is not loose or broken, then this is probably a problem with the internal circuitry of the brake controller and it will need to be replaced.
I have included an FAQ article on brake controllers and a video on testing a brake controller that might be helpful as well.
Daniel Z.
7/21/2020
Hi, I installed my Tekonsha Prodigy brake controller in my 2007 Escalade. I pulled the wires down from under the dash and hooked them up according to etrialer.com'structions and the instructions on the label wrapped around the wires. I also hooked up the wires to the studs under the hood. Checked the fuses for the studs and all looks good. The controller shows a "C" for connection when it is hooked to the trailer and the brake lights work on the truck and trailer. However the electric brakes will not engage when the pedal is depressed. I can get them to engage by applying them manually with the lever on the brake controller. I used a test light on the wire coming from the brake switch and there is no signal there even when the pedal is pressed. First thing I did was go buy a new brake switch. I changed that and still I have no brake signal. Any suggestions or help would be great.
Chris R.
7/27/2020
Chuck
5/17/2024
Hello, Will a bad brake light switch on the brake pedal cause the control to not work properly? My trailer brake control was working until my brake light switch started malfunctioning. Also, I had the same results with my other trailer brake control. Thank you.
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Ed
2/1/2020
2014 F250 Super Duty. I removed the brake pedal switch and looked for a red wire in and around the switch. There isn’t a red wire. There are 4 wires going into the switch. White/red, purple/orange, black and purple/white. There are no other wires connected to the switch or any empty connector for another wire. Suggestions?