Troubleshooting 2003 Toyota Tundra Trailer Brake Light Always On Hot

Question:

I forgot to tell you that the lights are on even if the truck is off. No other lights of any kind are on. The running lights on the truck are not on. Two places have said it is factory. So in other words. I would have to unplug the trailer evertime I’m not driving.

asked by: Brooks

Expert Reply:

The prong next to the ground on a 4-way flat is for trailer running lights. It should give you a light anytime your vehicle is running for trailer running/parking lights. If it is activating your brake light, then there most likely is a wiring issue and that can be on your vehicle or your trailer. Since there is not a factory 4-way available for your truck model year, we know there isn't a relay issue.

The brown wire is your running/park/tail lights. The yellow wire is the left side brake and turn signal. The green wire is your brake and right turn signal. The white is your ground wire.

You can test these functions using a circuit tester like # PTW2993. If you determine the issue is on your vehicle side, it is very likely that you have an improper splicing or a bad converter box. You can use the 4 Pole Harness and Hardwire Kit - Includes Tester # C59496 if your splicing is correct when tested and yet your harness is not accurate.

expert reply by: Jason S

Brooks

11/16/2017

Jason S.

11/16/2017

Interesting. Well, there is a work around to help you out. You can install the Tow Ready Battery Isolation Solenoid # TR118665 connecting the left side to your tail light wire, and the right side to the same wire leading to the trailer connection. Then you just add a wire that is spliced into 12V power only when the vehicle is on. This will give it the connection needed to turn off when you turn off your vehicle without unplugging your trailer. I've attached a video to assist.