Troubleshooting Trailer Wiring Where Only Side Clearance Light Illuminates

Updated 12/22/2025 | Published 10/14/2024

Question:

I have a utility trailer which I just ran a new wiring harness and added new LED taillights. The side light on the taillight is all that is lighting up, if I am not mistaken when the side light has power the taillight running light should have power as well, but it does not light up. I have power to both sides and grounded as well, the test light shows both sides have power, and it will blink when turn signal is engaged the test light blinks. The tow vehicle is working properly I just towed my boat and all lights work properly. Any suggestions to remedy this issue? Thanks

asked by: Jeff R

Expert Reply:

Hey Jeff, it sounds like an insufficient ground since only one light will power up and you have signal running to the lights. Since it is affecting all lights I would assume it's the main ground wire from the 4-way that should run to the trailer frame.

expert reply by: Jameson C

Jameson C.

12/22/2025

Hey Jeff, did checking the main ground from the 4-way connector fix the issue with your trailer lights? Knowing what solved it could really help others chasing similar wiring problems.