 1999 Ford Windstar - Electrical Problems
I recently had a similar problem, which I finally isolated by shuffling around the relays in the driver's side under-dash fuse box. Six relays at the top of this fuse box are identical. Isolate the relay controlling the door locks by pulling one relay at a time. Swap the suspect relay with one of the other five. If this isolates your problem, the replacement relay is ~$10 from Ford. I also recommend you check all relays and fuses regarding your power window problem as well. You can order an owner's manual (or a service manual) from the dealer. If you want to be thrifty, call some wreckers and see if you can pick one up on the secondary market. | 
