Troubleshooting Tekonsha 4-Way Kit Installed on 2010 Mercedes Sprinter

Updated 10/27/2025 | Published 03/09/2025

Question:

I just installed this kit on my 2010 MB Sprinter 2500 170WB but the passenger side turn signal isn’t working on the trailer. The running lights and driver side turn signal both work fine, and the passenger side turn signal still works on the van, but doesn’t pass through to the trailer. I also hear an on and off buzz from the controller box from the kit when the passenger turn signal is on. Any idea what might be going on?

asked by: Seth B

Expert Reply:

Hey Seth, if you disconnect the trailer from the Sprinter 4-way does the buzzing still happen on the # 118650? If so that would indicate either the connections are solid for the trailer wiring kit or the converter box has an internal short and would need to be replaced. If the buzzing goes away the problem is the wiring of the trailer.

I would first check the pins of the 4-way for dirt or corrosion and clean as necessary with sandpaper. Then trace the wiring up to the light assemblies and fix and shorts you find as needed.

expert reply by: Jameson C

Jameson C.

10/27/2025

Hey Seth, what ended up happening with the T-One wiring harness on your Sprinter after you checked the trailer connection and cleaned the 4-way pins? Knowing what fixed the buzzing or signal issue could really help others troubleshooting similar wiring problems.