how to test wiper motor
you might have a dud...with your multi-meter check for OHMS at the wiper motor itself....you'll have to unplug the connector...and the thing will probably have four wires, but there should be continuity between at least two of the lugs~
if you've access or want to buy a "Power Probe" you could juice the goose to see if it's movin'~
...else would have to blame the wiper switch~ https://www.google.com/#q=2000+ford+windstar+windshield+wiper+switch&t bm=shop
If you want to check to see if the wiper motor is bad, you have to remove the plug connected to it and see if there is power to any of the terminals of the plug. To check you will need a multi-meter. Set for greater than 12v. Turn the key to the on position and turn the wipers ON. Take the positive (red) lead and touch each of the plug terminals while holding the negative (black) lead to a nearby ground (usually on the firewall). If power is noted on 1 or 2 terminals (out of 4) your motor is probably bad. If no power is noted, the culprit is probably 1 or both the relays located in the power box under the hood OR the fuse in the passenger compartment (usually on the drivers side but can be on the passenger side on the side of the dash). If you have AC, that relay can be switched with the wiper relay to check relays. (They usually are the same)
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