Troubleshooting Brake Controller that Only Works When Headlights are On

Question:

I installed the Tekonsha Primus IQ brake controller on my 2012 Toyota Highlander. It did not have a factory installed harness, therefore I had to run the wiring myself to the battery and to the back of the vehicle. My question is whether or not I have properly installed it as the brake function is only available when my headlights are on. When I attached the red wire from the brake controller to the blue brake switch signal, could I have gotten that wrong? Everything else seemed to go well. The brakes do engage on my trailer when I brake, as well as when I engage the manual knob. This only works when I have my headlights on. Thank you for your help!

asked by: Kevin G

Expert Reply:

The problem is definitely the wire you used to attach the red wire of your brake controller to. The circuit you are currently using for some reason only has voltage on it when the brakes are applied with the headlights on. You need to keep testing the wires of the stop light switch until you find the circuit that sees voltage when the brakes are applied regardless of the headlights being on or off.

I attached a help article on hardwiring brake controllers like what you did.

expert reply by: Jameson C