You are describing it just fine. As long as the trailer is going down hill, it will not engage the brake. But once you start going uphill, the brakes will kick in and keep you from moving back. I have a Chevy, and I have to flip the 5 flat connecter (like BCB has said), with lights on, before I can back my neighbors boat up the driveway to his garage. I now have a 4 flat/5 flat combo to 7 round adapter. Which hopefully means I dont have to worry about it any more. It sounds like you need to relay switch that Fords are lacking.