Truck/Trailer Brake Lights Come on with Trailer Connected and not Using Brakes, 2001 Toyota Tundra

Updated 10/04/2010 | Published 09/30/2010

Products Featured in This Question

Hopkins 7-Way RV Style Connector with Molded Cable - Trailer End - 8' Long - RV Standard

(925)

$46.90

T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector

(110)

$62.81

Hook Probe Circuit Tester

(61)

$13.33

Question:

Im baffled by a trailer wiring issue, and from searching online, you guys seem to really know your stuff. Any way you could help? With my truck running lights on factory tow pack, and while in park, my truck and trailer brake lights come on, when I plug in my trailer. When I press the brake, they get a little brighter, but will not return to a normal, running light configuration. When I unplug my trailer, my truck lights return to normal. Im stumped... Thanks!

asked by: Josh T

Expert Reply:

From what I have been able to gather, the 2001 Toyota Tundra did not come with a tow package that included trailer wiring connections. This could mean that it was done aftermarket and could have been wired incorrectly by a previous owner. Or there could be a bad ground issue causing the malfunction. I recommend checking the ground connections on the truck and trailer side connectors. They will need to be clean and free of corrosion.

I spoke with one of our installers about this problem. He suggested that if your trailer itself has a battery and it is mis-wired, it could be back feeding through the truck wiring causing the lights to come on. You would just need to check the wiring on the trailer and see where the trailer side is sending power through the wrong way. I would test the trailer side pins without the trailer connected and see if any of them are putting out voltage which would indicate a back feed. You will need a circuit tester like # PTW2993.

If you are still having a problem, it could be the wiring harness on the truck. Your truck requires a specific style of harness that comes with a converter. What makes this harness even more special is that instead of connecting it in one stop at the rear of the vehicle, there is another connection that needs to be made under the hood between the battery and the fender. Take a look at Tow Ready Custom Fit Vehicle Wiring, # 118378, to see both parts of this harness.

This trailer wiring harness includes an in-line fuse in the connection under the hood. Some vehicles have a harness already installed that has a 30-amp fuse in it. If installing the above harness, this factory one needs to be removed. It uses a 30-amp fuse and the new one only requires a 10-amp fuse. I have included a link to the installation details below.

expert reply by: Michael H