Try moving the tilt wheel up and down and retesting the wipers. Generation 1 Sport Tracs are notorious for not having enough slack in the wiring harness that runs up through the steering column and you can have irratic operation of everything that goes throught the steering column including ignition, start, accessories, wipers, turn signals, horn parking lights, head lights, tail lights, and cruise control Yes, even the taillights go through the steering column.
You may have to remove the lower steering colum cover, to find the connector that holds nearly all the steering column wiring and make sure that none of the wires have pulled out or broken, and be sure to pull up a little extra slack so that using the full up/down adjustment of the tilt wheel does not pull the wires that go through the connector.
...Rich