Troubleshooting Trailer Lighting That Stops Working When Running Lights Come On  

Greetings eTrailer staff. Quick question: What are the probable issues causing the trailer signal/brake/running light to not properly blink while the running light is on? Before you answer, Ill provide you the parts and combos of issues for your evaluation. Parts: Item 118509 T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector Item HM48133 Hopkins 4-Way Flat Trailer Connector w/ LED Test Lights - Trailer End - 24 Item 3375601101 Trailer Wiring Junction Box - 7 Color Coded Terminals - ABS Item STL78AB Optronics LED Trailer Parking Light with Turn Function - Submersible - 10 Diodes - Oval - Amber Lens Installation of all items without any problem. Wires are hooked up according to the provided trailer diagram. White wires are connected to the two LED Item STL78AB as ground wires for it to work. White wire from the 4-way connector are connected to the trailers existing Groundinch location. This is for both the LEDs and the 4-way trailer end connector. Vehicles T-one wiring harness is grounded to vehicle. The fun time... Baseline scenario: Before I upgrade the wiring, Items 118509, HM48133, and Item 3375601101 works flawlessly without any problem using the old original wires on the trailer. ** Taking the same existing wiring layout, upgrading the flimsy 20-gauge wires with the heftier 14-gauge wires, encasing them inside the 1/2-in for weather protection, the new wires are installed exactly the way the old wires were installed, with additional white wires to support the new LED lights Item STL78AB. Scenario 1: I dont connect up the running light line brown, and the brake and signal lamp works perfectly. I can have my cars running light on, and signal as well as brake lights work without any issue with all lights on the trailer, WITHOUT the running light. The moment I connect the running light brown wires together, running lights are on, but brake and signal lamps wont work. Its purely running lights that are on. Wires are check over and over again to ensure proper wire connections. Scenario 2: I thought adding the two additional LED lights Item STL78AB may be the case. I removed them from the wiring. Disconnect the ground wire at the front trailer. Problem is the same as the Scenario 1. Not quite sure what happened. Any insight is greatly appreciated.

asked by: Nam N