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What are the Red and Black Wires For on a 7-Way Trailer Connector


I have seven wires in my trailer harness. I understand where all wire go/do .My confusion comes from the black and red wires... assuming in this case red is battery, what is black? Thanks in advance.


Helpful Expert Reply:

Typically, the black wire is 12 volt power and the red wire is left turn/brake lights. But you cannot always go by color. If the wiring in question is on the trailer side then there are two ways to determine which color wire does what function. You can physically trace the wires from the connector to where they terminate to discover their functions. Or you could apply power to each wire using a separate 12 volt battery and see what light or function turns on.

If the wiring is on the vehicle side then you can use a circuit tester such as # 40376 and test the pins on the connector while someone sits in the truck and runs through all of the functions.

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