mich800 the lower voltage is pressing the brake, the higher voltage is pressing the brake while also activating the manual control.
After talking with three Ford dealerships I gained no further help. So I went where I probably should have gone first - Google.
I found that the control was working correctly when the truck is still. Many states that have vehicle inspections were failing Ford trucks because the brakes would not lock down during their inspection. Ford issued a (pdf) explaining to them how the control works. With the truck stopped the control only sends a small amount of voltage/amps to the brakes to assist with a smooth stop.
So now I have to figure out how to get my brother-in-law affixed to the side of the trailer so we can check the voltage at that wheel while going 20 mph and then throwing on the brakes to see if we can lock them up. Us good-old-boys should be able to dream up a neat way of doing this. lol
Anyway thanks for your comments