Installing 4-Way Trailer Connector to Trailer with 5 Wires With 2 of Them Being the Same Color

Updated 05/24/2019 | Published 05/23/2019

Question:

My trailer connector has 4 wires, but the wiring has 5 2 yellow wires. What should I do with the extra yellow

asked by: Thomas K

Expert Reply:

Even though the yellow wire is typically associated with the left turn/stop lighting functions I think your 2 yellow wires are for the tail/running light functions and you need to splice both of them to the appropriate pin (see attached picture). Since the standard trailer wiring colors are more of a suggestion than a requirement the wire colors can vary. If you check out the Optronics # A35W42B trailer wiring harness you can see that there are 2 brown wires. This is so that you have 1 wire running down each side of your trailer to make connecting your marker and tail lights much easier.

The best way to find out where to connect these though is to take a 12V battery (like what is in your tow vehicle) and after grounding the negative terminal using the positive terminal to apply power to either of the yellow wires to see what function(s) each wire is connected to. Then you can correctly and confidently install each wire to your 4-Way Flat connector.

expert reply by: Jon G