It could be any number of things. It could be the activation switch on the steering wheel has failed or it could be the deactivation switch on the brake pedal or it could be the control board or it could be the speed sensor.
If you are not inclined to diagnose it yourself than do as others suggested and take it to the Ford TRUCK repair.
I will say that the most common defect is the brake pedal switch or the activation switch on the steering wheel. If you are inclined to diagnose it then let us know and I might be able to help you out.