Troubleshooting Trailer Lights Not Working with Running Lights Turned On

Published 08/16/2023

Question:

I had a 7 wire to 5 flat on my boat. I’m replacing with 5 wire to 5 flat. I wired both reds to the new blue. Wired both L and R tail lights together under a butt connector and connected to Brown on the new 5 flat. Wired the L Turn to yellow. Wired the right Turn to green. White ground to ground. All good, however… Problem is, the Turn and brakes dont work if the Tail lights are on!? If I turn the truck lights off no tail lights then the signal and brake both work fine but when the tail lights are on I get no signal or brake! Any ideas? Thanks.

asked by: Shaun

Expert Reply:

According to our research you either have an insufficient ground, or you have way too many running lights on your trailer.

I recommend making sure your all of your wiring connections are nice and solid and that the grounds are securely connected to a clean, bare-metal surface. If that doesn't work then try disconnecting one tail light at a time to see if that reduces the amount of power being pulled to the tail lights enough that the other lights work correctly.

expert reply by: Jon G