Can a Bad Trailer Wiring Converter Cause Brake Lights to Stop Working?

Updated 09/01/2026 | Published 08/26/2026

Question:

I recently took my Prius with the tow package Ive installed from you to the dealer for a regular servicing. While there, I asked him about a blown fuse up near the conventional battery. He told me that it was working now, but that the brake lights wont work and he tracks it back to the computer module from your company. Can you help me?

asked by: Brian C

Expert Reply:

Hey Brian, thanks for reaching out. It is rare, but the converter module in the wiring harness can go bad. Based on what the dealer found, it sounds like the module is still communicating with the car but is no longer sending the brake light signal out to the trailer connector.

If they have narrowed the problem down to the converter itself, the fix is to replace the wiring harness. For that, you can use the Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector # C69KR. This gives you a new converter module along with the vehicle-specific wiring and 4-way connector, so you are replacing the entire affected portion rather than trying to repair the module itself.

Before replacing it, I recommend having the dealer verify that the vehicle's brake light signal is reaching the converter and that the problem is definitely on the output side of the module. If that checks out, replacing # C69KR is the route I recommend.

What do you usually tow with your Prius?

expert reply by: Jesse M