How to Determine Functions of Random Wire Colors for Trailer 7-Way Connector

Question:

My trailer had 3 black wires 2 red wiresa white and a green im confused how to connect 7 blade

asked by: Patrick

Expert Reply:

Although a lot of trailer wiring use the same colors, since there is no standard rule on what color wire needs to be used for which function it can be confusing when you have to do maintenance on trailer wiring.

The easiest way to determine which wire is for what function on your trailer is to use a 12V battery (like what is in your tow vehicle) and then run a ground wire for the negative terminal and a loose wire on the positive terminal. Then all you need to do is touch the loose wire to each of the wires that you mentioned and see what function it activates on your trailer.

If you don't already have a 7-Way connector for your trailer you can use the attached photo (from the linked wiring article) to connect your wiring to a 7-Way connector like part # PK12706.

An easier way would be to use a 7-Way with a junction box like part # HS381-9000. The junction box has terminals on the inside that are labeled according to functions. This makes it a lot easier to perform wiring maintenance in the future.

expert reply by: Jon G