Troubleshooting Tow Ready Trailer Wiring Harness # 118304 Installation in Toyota Sienna

Question:

I have part number 118304. In the description it says it includes the tail light converter. I plugged everything in per the instructions and I also watched the video. When my head lights on the car are on it causes the brake lights to illuminate resulting in no brake lights and no turn signals on the trailer. I also have part number 118301 which Im not even going to attempt if Im going to have the same problem. Any ideas what the problem is?

asked by: Justin L

Expert Reply:

Thank you for your recent purchase.

The two plug-and-play trailer wiring harnesses you have, Tow Ready part # 118304 for the Toyota Sienna, and # 118301 for GMC/Chevy and Isuzu pickups, both install inline with the pre-wired T-connectors to the vehicles' tail light wiring.

The problem with erratic light functions that you describe is most often related to a grounding issue. You can begin your troubleshooting by confirming that the white ground wire with ring terminal is firmly secured to a clean bare metal surface on the vehicle (preferred), or to an existing electrical grounding point for other vehicle wiring. Even a slight difference in the degree of tightness of the ground connection can affect performance. You can sand off the paint/primer from your grounding point if it is not completely clean and bare metal. Make sure the ground on your trailer connector is similarly affixed to a clean bare metal surface on the trailer tongue.

The other most-likely cause for this problem is that the trailer has too many running lights for the harness' capacity (which in the case of harness # 118304 is 2.1 amps per stop/turn circuit and 4.2 amps per tail light circuit).

I have linked you to a comprehensive troubleshooting article that details the steps you can take to isolate and correct the problem. It is possible that an issue in the trailer's wiring could be at fault, and this is why we suggest testing with a circuit tester to eliminate or confirm the trailer as the source of the problem.