There is a "module" in the engine-bay fuse panel (module is Ford's word, so I assume it's somehow different than a fuse...) that can malfunction and cause this....I had that problem on the 1998 that I used to have and the put a new "module" in and immediately solved the problem. Maybe you'll get lucky and it will be that simple.
P.S. What I'm talking about is one of the larger square-shaped pieces in the fuse panel...about an inch by an inch.....
P.S. What I'm talking about is one of the larger square-shaped pieces in the fuse panel...about an inch by an inch.....