hello there,
We are talking about a Winstar correct? You need to lube the back latch of the door, its kinda hard to get to, open the door and spray wd40 into latch [soak it down real good] and open and close door a dozen times or so. If that doesn't do it there are contacts on the front side of the door that you could try cleaning up.
You might want to wd40 all your latches just to prevent the problem moving to a different door
Senior Master Ford Tech
26 years exp with Ford Products, ASE Master Auto & Truck + advanced engine perf L1/L2 Gas & Diesel