Why are there So Many Different Trailer Connectors and Ways to Wire Them

Updated 05/22/2015 | Published 05/21/2015

Question:

just wanted to know why so many trailers are wired different semi trucks and trailers are allthe same so frustrating to hook up to someone elses trailer and something is different either the brakes lock up when you try to move trailer or something

asked by: Bob W

Expert Reply:

If you think we have it bad here in the states try going to Europe where they have a 7-Way that does the same things as our 4-Way and some kind of 13-Way to do what our 7-Way does!

In the US the biggest issue is the 2 different ways that a 6-Way round connector can be wired. The center pin will either be for electric brakes or 12 volt power. Usually when the brakes immediately lock up it is because the 12 volt circuit on the vehicle connector or adapter is wired one way and the one on the trailer is wired the opposite way. You would just need to swap the wire locations for 12 volt power and electric brakes in the trailer side connector.

The industry also changed from using a 7-Way round pin connector to a 7-Way blade style connector. You still see 7-Way round pins some times but they are usually on more heavy duty applications, commercial applications, or agricultural applications.

I have included a link to our help article on trailer wiring that covers the various connectors and how they are usually pinned out.

expert reply by: Michael H