Troubleshooting New Trailer Lights That Flash Both Side Taillights when Turn Signal is Activated

Question:

I got the complete kit with new wiring, new lights. Last year the truck side wiring was done. When I signal on one side or the other, both lights flash like they are on emergency flashers. I ground down the two light side surfaces to bare metal before attaching grounds. The front ground is fresh too. ?

asked by: Mikki B

Expert Reply:

First, I recommend testing the trailer connector at the rear of the truck to ensure that the wiring on the truck is functioning properly. You can use a circuit tester like # PTW2993 to test the pins at the connector, while a buddy in the cab of the truck runs through the functions of the connector. If the wiring on the truck is not working properly, you will want to take the truck back to the shop to installed it.

If the truck wiring checks out properly, then we know the issue is on the trailer's wiring. Since you said you've checked the grounds, it sounds like there could be a short caused by the left and right signal wires touching. This short could be anywhere on the trailer wiring, even inside the trailer-side connector. If the left and right signal wires are touching, this can cause the flashing you are experiencing on your trailer. You will also want to check the wiring or any pinches, tears, or other damage that could be causing a short.

expert reply by: Victoria B