F-350 brake module won't work

My father-in-law has a 2008 F350 with brake module problems. In order to get any braking power to his 34' camper/trailer, he has to set the controller up to the max setting. This gets him very little stopping power, but much better than a mid-range setting - which is nothing.

Problem seems to be related to the module operation, which looks at wheel speed in calculating the amount of voltage to apply to the brakes. We confirmed the brakes on the trailer work correctly by testing with 3 separate tow vehicles (none with the built in Ford controller). All seem to stop the trailer fine.

Ford dealer of course tells us there is nothing wrong with the built-in controller.

What is built into the logic of the factory controller that would not allow it to work correctly or could polarity be reversed or some poor connection that would cause this? We are about to add an aftermarket controller to fix a ford problem on a brand new truck.:eek7:

I would check the ground wires use an ohm meter and check the ground in the plug. Clean the connnections in your adapter with an ohm meter. I've found some cheap aftermarket units don't work correctly. My 1997 F-150 had factory towing package but it only had a plug you use to wire the brake unit.
The plug was close to the brake pedal. I would think your new unit should work and would start moving up the chain. First stop dealership owner at new vehicle cost with the economy he don't want you telling your friends to buy Chevy or Dodge diesels if they need a truck to pull a backhoe.