How To Find Stop Light Switch Wire For Trailer Brake Controller In 2015 Lexus RX 350

Question:

Where can I find an easily accessible stop light wire? It is equipped with a factory trailer package.

asked by: Chris B

Expert Reply:

The cold side of the stop light switch wire which a trailer brake controller gets connected to will be on the stop light switch itself.

You will want to start at the brake pedal of your 2015 Lexus RX 350 and work up towards the firewall. The switch will be touching the brake pedal arm or have a wire running to the pedal arm.

Once you have found the switch you will need to use a circuit tester like # PTW2993 to test each wire. The correct wire only has power when the brake pedal is pressed. When we installed the Tekonsha Prodigy P3 # 90195 in a similar 2013 Lexus RX 350 we found that the cold side wire was the yellow wire as you can see at the 19:00 minute mark of the included video.

I included a video of the # 90195 for you to take a look at.

expert reply by: Samuel C