The windshield wipers will not work if the 1990-1993 switch is used on the 1987-1989 harness. Testing with a multimeter will show you the wires that Ford chose to move when the design of the switch changes. All controls have the same wiring except the windshield wipers.
After the correct wires are determined, it is an easy task to remove the wires from the plug by pressing down on the tab on the front of the plug and sliding the wire out the back. Then, the wire can be inserted into the previously unused connection hole on the plug.
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