Troubleshooting Boat Trailer Lights That Don't Work When Vehicle Headlights Are Turned On

Updated 04/30/2020 | Published 04/29/2020

Question:

The lights on the trailer work properly with my headlights off when I turn my headlights on and turn a blinker on every light on the trailer blinks I’ve replaced mounting surface for the square tail lights with new metal and I have removed the small yellow running light brackets and cleaned the surface they bolt to and still no luck

asked by: Mj

Expert Reply:

It sounds like what you're describing could be an issue with the ground wire on the trailer-either a short or an insufficient connection. This is a common cause of lights working initially but then malfunctioning when another load is added to the mix. I would start with checking the ground wire on the trailer to make sure that it is firmly connected to a paint and corrosion free spot on the trailer; it would also be worth checking the ground wire on your vehicle's wiring harness at this time. This malfunction would still be possible with lights like the # TL5RK that are grounded through the trailer frame, since the malfunction would create issues on the power circuit receiving sufficient voltage-creating the flickering/blinking you're seeing.

I've linked a troubleshooting article that I recommend having a look at while going through these first troubleshooting steps, but let me know if that doesn't address your issue and I can give you a few other things to look at.

expert reply by: Erik B