Troubleshooting A Tekonsha P3 That Isn't Activating When The Brake Pedal Is Depressed

Question:

I have the Tekonsha P3 brake controller. I have a 2024 Toyota Grand Highlander. I hooked up it up and have control with the manual override. Although, no braking with the stoplight switch. I watched the video Tekonsha P3 ... 2019 Toyota Highlander and it mentioned a harness with an integrated diode, P/N 7865. I was looking and dont see this part on your website. I dont see any installation guidance stating that I need this for my Grand Highlander. Please help, Eric.

asked by: Eric H

Expert Reply:

Hi Eric,

The diode harness you're referring to has a diode on the red wire to prevent feedback when using the manual override and wouldn't solve the issue of your brake controller not activating when the brake pedal is depressed. You likely aren't tied into the cold side of the brake switch and will need to either retest the wires coming off the brake pedal with a tester # PTW2993 until you find the one wire that only has power when the brake pedal is depressed. Toyota typically has very small gauge wires that are hard to splice into so you could avoid testing each wire and just install a stop light switch # RM-751000 and run its output wire to the red wire on the brake controller wire harness.

expert reply by: Kevin C