Wiring Harness for 2026 Lexus TX 500h

Updated 05/06/2026 | Published 05/01/2026

Question:

I own a 2026 Lexus tx500h. I have the black box under the cup holder in the third row. I also have the plug in the back under the bumper. So which harness do I need? I understand there is one that is wired backwards. I don’t want to buy that one.

asked by: Jeff C

Expert Reply:

Hey Jeff! Use the connection under the cup holder, assuming that is on the driver side, and install the Curt # C56RV. There have been no reports with this wiring harness of backwards wiring so you won't have to worry about that issue on your Lexus.

What do you plan on towing?

expert reply by: Robin H

Curt C56RV
(click to enlarge)

Steve

5/6/2026

FYI….i installed the Curt C56RV in a 2025 Toyota Grand Highlander and when I applied the brakes, the turn signal would switch to the opposite side on the trailer. I.e. - Left turn signal would switch to the right turn signal on the trailer when the brake pedal was pressed. it worked fine when the brakes were not applied. I ended up buying Toyota’s version of the black box and that corrected the problem. Being that Lexus is built by Toyota, you could have a similar issue. Hope not.

Robin H.

5/6/2026

@Steve if it only happened when you applied the brakes that sounds more like a bad ground and not a reverse wire situation.

Steve

5/6/2026

@RobinH That is what I thought but confirmed the ground was good on my end. Being that the Curt box is sealed, I could not confirm if it was an internal issue with it. I ended up buying the Toyota black box and all the problems went away. FWIW…..if you look back at my posts from 2025, I had this same conversation with one of your co-workers.

Don

5/6/2026

I ran into the same backwards wiring as well. My fault though. I used two different kits. One for the 4 wire plug in the back and a separate kit for the box in the side panel. My recommendation is to purchase both items in the same kit. Shouldn’t have any problems with the wiring then.