How to Determine What Running Light Wires Are on Trailer

Question:

My running lights are not working on my cargo trailer. I have a 7 pin plug and I can’t tell if the green wire or brown wires are the running lights? Everything I see is a mixed review. I found one black wire that was cut and fixed it. Found a spot in the green wires where they carry 12v and stop and to 3 bolts so I believe there is corrosion somewhere there. But if the green wires aren’t the running light wires. Then what is. Everything else is working fine.

asked by: Taylor B

Expert Reply:

You can't use wire color to determine what the running light wires are; you have to use a circuit tester like the Cordless Circuit Tester # PTW2979.

You mentioned corrosion, and generally with running lights it's either that or a bad ground, so if there is excess corrosion you can replace your 7-way. Otherwise, make sure all of your grounds are attached to bare metal surfaces and free of any paint, dirt or corrosion, and I would wager that will fix the issue.

I have added links below to a pair of help articles on trailer wiring, including a troubleshooting guide for you to take a look at. Additionally, to help prevent any type of corrosion in your connector, and increase its durability and lifespan I highly recommend using Dielectric Grease for Electrical Connectors # 11755.

expert reply by: Kyle S