For starters, the oem brake controller on your 2009 Ford F-350 has a proportional design which means it would not put out 12 volts or anywhere close while using the brake pedal at a stop. That said, if you are having issues with weak brakes while in motion then there could be a few other issues. The first thing I recommend you do is make sure the brake controller is turned all the way up and then start testing the wire from the vehicle connector all the way back to the magnets with the... view full answer...