Troubleshooting What Wiring Harness Will Work for a 2023 Lexus RX 350  

Question:

Expert Reply:

Hi Tiffany,

So, issues with the trailer wiring for a 2023 Lexus RX 350 is a common experience that a lot of people have due to an electrical system change Lexus made on the new RX models. The brake and turn signals are sent down separate wires so a powered converter module is required to protect the vehicle's wiring and provide enough power for the trailer lights.

If your vehicle has a factory tow package then a pre-wired plug-in connector like the Curt T-Connector Vehicle Wiring Harness for Factory Tow Package w/4-pole Flat part # 56083 is what you'd need to plug directly into the OEM tow package port that is behind the rear bumper on the driver's side.

If your vehicle does not have a factory tow package, then the vehicle uses a low-voltage, computer-controlled lighting that can't support a plug in harness. Instead, you'll need a wiring harness with a powered converter to read the taillights, pull power, and generate a trailer signal. Currently, we don't offer a custom plug-in harness with a powered converter. However, the most common fix is a universal harness like the Curt Powered Taillight Converter w/4-Pole Flat part # C59236, it requires splicing into the lights and running a 12V power wire to the battery. This will give power to the trailer light circuit and get the trailer lights a useable signal. From the issues you've described, it sounds like a black power line wasn't run to the battery or if they did use a plug in harness, it didn't have a powered converter.

I've attached a video showing an installation of the Curt Powered Taillight Converter w/4-Pole Flat part # C59236 on a 2024 Lexus RX305H for reference to help trouble shoot.

Do you happen to know the brand or part number of the wiring harness that was installed on your Lexus currently?

expert reply by: Claire H

0

Dane

4/10/2026

On the wiring kit I bought you need to take one wire not sure what color now. But wire into fuse box with a fuse able link so you have power to the rear to run taillights. If dealer didn't do that good reason why it won't work. Be sure you get the directions for wiring from the dealership. Good Luck

Joe S.

4/10/2026

@tiffany Go to those hole in the wall looking places where they do speaker and audio systems for cars ask if they can do it it’s a custom work around a dealership I assume just won’t

Claire H.

4/10/2026

@Dane You're totally right that the harness will not work if the one wire (the black wire) isn't run to the battery. With that not wired up the harness won't work at all or will act wonky at best.

Claire H.

4/10/2026

@JoeS Mom and pop shops are usually some of the best help out there! Nothing like having an expert in your own neighborhood to help you out!