Troubleshooting Brake and Turn Signals Not Working on Trailer

Question:

Have a 2001 tundra I just replaced the wire harness everything looks good still having issues with my Lights on my trailer.

asked by: Quentin H

Expert Reply:

I'm not sure which wiring harness you replaced but we can cover the trailer and the vehicle side for troubleshooting. The first thing I would check is your 4-way connection. Make sure both connectors are clean and free from debris, and make sure they are not damaged. Once this is done, I would go ahead and check out the connection on the vehicle side using a circuit tester like the # PTW2993.

You want to test to see if the brake and turn functions are working properly on the vehicle connector. If they are, then you know it is on the trailer side, if not, then it is on the vehicle side. If it is an issue on the trailer it is more than likely a bad ground connection somewhere. Make sure your ground wires are secure on a clean, bare-metal surface. Since your running lights work it is unlikely that it is the lights themselves. The only other thing you could do on the trailer side is look for a short and repair it.

If it is on the vehicle side it could be a number of things. If you have a tow package it might be the fuses. You should be able to locate the fuse diagram in your owner's manual or on the fuse box itself to identify the fuses and check them. If you have an aftermarket wiring harness like the # 118378 then it may also be the fuse located in the fuse holder. Also, if you have the Tekonsha harness or one like it, I would try unplugging it and plugging it back in to make sure it is seated properly.

If it is not the fuses and you have the factory wiring harness and tow package then I would take it to a dealer to get checked out. If you installed a wiring harness like the Tekonsha go ahead and test the same wires before the converter box. If you have a good signal here it is the converter box and you will have to replace the wiring harness.

If not, then it is again a vehicle wiring issue since no signal is getting to the plug. You could attempt to inspect the wiring yourself for a short but more than likely you will need to take it to a repair shop and have them look at it.

expert reply by: Robin H