Troubleshooting 4-Pole Flat Connector With No Brake Light Signal

Updated 03/14/2025 | Published 03/07/2025

Question:

Which terminal on the T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector is for the brake lights? I only seem to have running and turn signal lights. The single male terminal is the ground. I have a 2018 Rav4 with amber turn signals.

asked by: Leonard D

Expert Reply:

Hello Leonard, thanks for reaching out. On a typical 4-flat like the Tekonsha # 118578, the yellow wire is for left turn signal and brake, then the green wire is for right turn brake. The way I remember it is the word yellow has the letter "L" in it and L is for left. Easy right? Then the brown wire is tail lights and white is ground.

If you aren't getting proper output at the converter module (which it sounds like you aren't), the first step will be to take a wire tester and check each wire going into the converter module. Check the yellow and green wires and make sure the input signal is correct. If the input signal is there, but no output, this means the converter is bad. If the input signal isn't there, this means there is an issue on the vehicle side. Bad modules are rare but not unheard of.

If you can check those wires, and reply below with your findings, I will help you with the next steps. Or feel free to reach out with any additional questions.

expert reply by: Jesse M

Leonard D.

3/14/2025

I think I figured it out. The trailer only has running lights and brake/turn lights. The turn signal (brighter) light if activated, will turn solid (not flash) when the brakes are applied. Whereas my Rav4 has dedicated amber turn signal lights, the trailer does not. I believe my trailer module is working properly Thanks Len Davis