Check to see if your chassis is part of the big Ford cruise control brake switch recall. I don't know if the F53's were (the E series vans were, as were the F series trucks, so I suspect they might be), nor exactly how far back it goes.
At any rate, the recall involves a switch on or near the brake master cylinder that is actuated by hydraulic pressure when the brakes are applied and presumably cancels the cruise control. For some reason, it's hot all the time, even with the ignition off, and was inadequately fused. The switches had a tendency to corrode internally eventually and sometimes short out, causing fires. Since the switch was wired hot all the time, this could be a fire hazard with the vehicle parked.
I'm guessing that perhaps this switch, if you have one, may be bad or if the recall was done, which I think mainly involved adding a fuse inline, the added fuse for it has blown.