This is a very common problem on most Ford, Lincoln and Mercury products with power mirrors. A vehicle will come in with a complaint of the power mirror does not work in one or two direction. The simplest test is to see if both mirrors react in the same manner. If they do I go with the odds that the switch is faulty because it is highly unlikely that both mirror assemblies would have the exact same problem. I also keep a test switch or two around to save time. Anyhow this is the procedure for changing the power mirror switch on a 1998 Ford Windstar.
The switch is obviously located on the driver’s switch panel.
You will first need to remove the interior door handle trim panel.
Using your fingers or a flat tool, lift the forward edge of the trim panel up.
After loosening the front edge continue around and remove the trim panel by pulling it forward past the door handle.
Next lift the front edge of the switch panel to release the spring clip. Then pull forward to finish releasing it from the door panel.
With the panel removed you will now be able to access the wiring harness connectors.
Unplug the power mirror switch harness connector by depressing the thumb latch and pull it from the switch.