Troubleshooting Trailer Tail Lights That Blink Together and Shut off When Brakes are Applied

Question:

when turning on left turn signal both lights will flash, when turning on right turn signal both lights stay lit. Finally when applying brakes , both lights will go out. I have sanded down too bare metal nothing changes,just wondering if you have anymore suggestions ?

asked by: Freddy E

Expert Reply:

The first thing you will want to do is test the 4-way of the tow vehicle that you installed with a circuit tester like part # PTW2993. See the video I attached to see how this is done. This will tell you if the problem is on the vehicle side or trailer side of the wiring.

If the problem is on the tow vehicle then you will want to check the back of the connector for cut or exposed wire that could be causing a short and fix as necessary.

If the problem appears to be on the trailer the first place to check would be the grounds of the light assemblies. It sounds like you already did this though. Any time lights shut off when the brakes are applied it typically means the problem is the grounds of the trailer. You will want to inspect the wiring of the trailer from the trailer connector all the way to the light assemblies looking for any cut or exposed wire that could cause a short and fix as necessary.

Since both turn signals blink with the left blinker that is a pretty good indicator that at least those two circuits are shorting out to each other.

I attached a couple FAQ articles to the right for you to check out as well.

expert reply by: Jameson C