How To Replace a 4-Way Trailer Connector with a 7-Way Trailer Connector

Updated 04/10/2019 | Published 04/08/2019

Question:

Hello, Im trying to wire up a 7way trailer plug. The trailer had a 4 way plug on it before. I tried hooking up the wires to the new plug with no luck. I was able to get the left light to work when the 4 ways were on. But as soon as turn the key on with the 4 ways I get no power. I tried looking for a schematic that would explain it better but got more confused. lol. I sure could use some help. Thank you!

asked by: Dan

Helpful Expert Reply:

The best option we have for you to upgrade the 4-way trailer connector on your trailer to a 7-way trailer connector is with the Trailer Wiring 7-Way Upgrade Kit part # HS381-9000. Once you have this all you need to do is run the wires from the trailer lights to the junction box and then from the junction box to the trailer connector.

Inside the junction box, the terminals are labeled by both wire color and function. However, when running the wires from this trailer connector to the junction box you will need to do so by function, not color. This will be the case when running the wires from the trailer lights to the junction box as well. I recommend you apply 12 volt power to each of the wires on the trailer to see what function the wires represent. Once this is done you can then attached them to the junction box using their function.

It sounds like you may be trying to match the color of the wires together now which is most likely why you are running into issues. I have attached a helpful trailer wiring article for you as well.

Trailer Connector to Junction Box:

White Wire to Ground Terminal
Red Wire to Left Turn and Brake Terminal
Brown Wire to Right Turn and Brake Terminal
Green Wire to Tail Lights Terminal
Blue Wire to Brake Output Terminal
Black Wire to 12 Volt Terminal
Yellow Wire to Auxiliary Terminal

Junction Box to Trailer Lights:

Ground Terminal to (Test for Function) Wire
Brake Terminal to (Test for Function) Wire
Brake Terminal to (Test for Function) Wire
Tail Lights Terminal to (Test for Function) Wire
Brake Output Terminal to (Test for Function) Wire
12 Volt Terminal to (Test for Function) Wire
Auxiliary Terminal to (Test for Function) Wire