First you need a a controller, I have a PRODIGY Brake Controller. I like it, a lot rated up to four axles and has 3 different boost settings.
You can pick one up from here,
http://www.brakecontroller.com/?gcli...FRRhnAodSDg5hQ
If you order from them you get a free harness that allows you to plug in the controller to the truck with out having to use the one that you got with the truck with the lose ends on it.
The plug on the truck for the brake controller is right behind the OBI II port behind the dash. You have to lay on the floor to see it, it should be taped to one of the main wire looms running across the dash.
Here is were the plug is
Here is were I mounted the controller on mine. there is actually a steel plate were you can screw your bracket to and it works out perfect.
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2006 F-150 4X4 Supercab XLT 145" WB 5.4 3.73LS
-Line-X; Highland Rubber Floor Mats; Prodigy Brake Controller; Ultra Remote Starter; Pioneer 2900MP Head Unit; Memphis 15-PR572 Speakers; Pilot Auxiliary Backup Lights; 2008 Telescoping Trailer Tow Mirrors; 2007 load trail utility Trailer
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http://s221.photobucket.com/albums/dd93/4x406f150/