Troubleshooting a 4-Way Connector on a 2025 Grand Highlander Changing Sides on the Turn Signals

Updated 03/18/2026 | Published 05/27/2025

Question:

I installed a 4-pin wiring harness into my 2025 Toyota Grand Highlander, using the Curt T-connector wiring harness C56RV. Everything appears to be working properly except when I apply the brakes, the signal light switches sides on the trailer only. In other words, I turn on the left turn signal and when I press on the brake pedal, it switches to the right turn signal. Take my foot off the brake, and it switches back to the left turn signal. It happens whether it is left or right turn signal applied. Vehicle turn signal lights are not affected, only trailer lights. I initially thought it was a trailer wiring problem so I disconnected the trailer and used a test light with the same result. That tells me it is coming from the vehicle. I watched the video where your installer Bruce installs this item into a 2024 Grand Highlander and at the end of the video when he shows the light status with the tester, it too changes sides when he presses the brake pedal. Is there a solution as to why my signal lights changes sides when the brake pedal is depressed? Thanks in advance.

asked by: Steve C

Expert Reply:

Hey Steve. Normally I would say you're describing a bad ground but we've had this issue with the wiring connectors before when Toyota first launched the Grand Highlanders. Does your 2025 Grand Highlander have the factory tow package?

According to Curt their T-Connector Vehicle Wiring Harness item # C56RV you purchased will fit the 2025 Toyota Grand Highlander with or without the factory towing package. The same connector is located underneath the cup holder. However, it work right 100% of the time because Toyota has a OEM module included in the towing package they don't include on the models without. It's pn PT725-48241 and is located forward and down from the connector.

We do not carry this part which is why we list the Curt T-Connector Vehicle Wiring Harness item # C56RV as only being compatible with the 2025 Toyota Grand Highlander's that have the factory tow package.

If you have any additional questions, go ahead and click on the box below that says Reply to Jerred H and I'll be happy to answer them.

expert reply by: Jerred H

Connector
(click to enlarge)

Steve C.

6/2/2025

Jerrod, I thought bad ground as well but confirmed it was good. My GH does not have the tow package. For what it is worth, the tow package consists of a heavy duty radiator, transmission cooler and tow hitch receiver only. The Toyota OEM module (PT725-48241) is an additional purchase and plugs into the same connector that the Curt module plugs into. There is no second connector to connect both modules. I am removing the improperly working Curt module and replacing it with the Toyota module. For those looking to go in this direction, I've searched several Toyota parts sites for P/N PT725-48241 and have seen web pages telling me it is an exact fit for my GH and other sites saying it does not fit. I spoke with my local Toyota dealer and had their tow package installation tech look at it and they have confirmed that P/N: PT725-48241 is the only module that Toyota makes for the model years 2024 and up for the Grand Highlander. And it is less expensive than the Curt module. In my search to find answers to this issue, I've seen others who have had issues and had reached out to Curt. Their response was that it was a GH wiring problem. All these vehicles have the same basic wiring so I am very skeptical that it is a GH wiring issue. Thanks.

Jerred H.

6/2/2025

@SteveC Sounds like you've got it sorted out. I do know that Curt is aware of the problem and are the only ones with an aftermarket option.

Steve C.

6/2/2025

Jerred H., I think I do have it sorted out. Will report back if I find the Toyota OEM module does not fix the issue.

Steve C.

6/9/2025

@SteveC Confirmed that Toyota part PT725-48241 works for the 2025 Grand Highlander. Toyota provided full instructions on which panels to remove, mounting points & bolts, as well as fuse and where it is located.