You can check the brakes by using the emergency brake switch instead of the truck umbilical.
Don't leave the pin out for any long length of time but if you carry a compass around to the axles, and if the magnets are powered, it should swing the compass needle. If you have the wheels off the ground, you can also turn a wheel to check shoe->drum contact.
As was mentioned, adjustment is key to good brake operation.
BTW, the Ford brake controller is an inertial controller, i.e. truck needs to be moving for the brake pedal to send power to the umbilical.