Anyone familiar with trailer wiring? I am installing an under dash brake controller and need help with the wiring. My truck has the 4 way flat plug that hoooks to the trailer, and my new trailer has a male 7 way round plug. Which wire of the 4 way is the one from the electric controller? I have an adapter to go from the flat 4 way to the round 7 way and need to find out which wire on the 7 way plug is used to control the brakes. Thanks

 

there is no brake wire on the flat four wire plug. look up under the dash to the left of the steering column for a coiled up blue wire.. that is the wire for the brake controler, but you have to get the round plug wired correctly. Just plugging your flat 4 wire plug into it won't get power to your brakes.

 

I have a pigtail from the controller that plugs into a plug next to the steering column. I thought with a factory tow package the brake controller wire should be somewhere near the bumper? I will open the 7 way plug and see which is the wire from the brakes.

 

Here's a wiring diagram for the connectors. It's drawn looking at the front (non-wire end) of the plug. http://www.accessconnect.com/trailer_wiring_diagram.htm