I have trailer that I re-wired. all lights work with the exception of my left rear light. When the headlights are on, all lights are on except for the left rear light. when I touch the brakes, the brake lights on both sides of the trailer come on. When the headlights are off, all lights on the trailer are off. When I put the brake light on, the brake lights on both sides of the trailer are on.
I checked the light bulb and it appears that both filaments are still intact.
Hi, If your running/marker light is out on that one side then using a test light, test for power going into the left side light assembly for the running light. If there is no power there trace the circuit back to the power wire that goes into the right side light and run a wire from that light. Just make sure you identify the correct wire on the right side light. Also make sure you have a good ground and if it is a dual filament bulb, that it is tight in the holder and the bulb is good. I hope this helps. Thanks for using JA
1995 Wyo-tech graduate 17+years shop/field experience/on all major brands of heavy equipment and trucks.