Why Does A Trailer Wiring Harness Have Two Brown Wires?
Updated 10/27/2025 | Published 03/12/2025
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Question:
Trailer harness with yellow and brown going down one side and green and brown down the other. One light has a yellow wire and two brown wires, the other has a green wire and two brown wires, so my question is what does the second brown wire on each light connect to ? I’ve wired it connecting both brown wires from the light to the harness and no lights are working. I’ve grounded the harness correctly at the tongue.
asked by: Wade F
Expert Reply:
Hello Wade, thanks for reaching out. Generally when a trailer harness has two brown wires, they are both running light wires. This is because there are running lights on both sides of the trailer so having the second wire makes things more simple. What I would do is add a junction box like part # 3430001-JBK. This way you can run all the brown wires together and keep your connections nice and neat.
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Product Page this Question was Asked From
25 Ft 4-Way Trailer Wiring Harness - Wishbone Style - 25' Ground
- Trailer Wiring
- Trailer Connectors
- Trailer End Connector
- 4 Flat
- Plug and Lead
- Optronics
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Jesse M.
10/27/2025
Hey Wade, how did things go after you tied the brown wires together using the junction box? Knowing whether that cleared up the lighting issue could really help others sorting out similar trailer wiring setups.