Windshield Wipers Relay on Ford Mercury 1991

There is no wiper relay as such. Note the diagram. See the fuse in upper right, did you check the fuse? Not only check the fuse, use a test light and check voltage on fuse, goes hot with the key on. See the solid blue wire at wiper motor, it's hot with the key on, use a test light to check voltage. You see the hi and lo speed at the blower motor, see the wire color, blue with tracer color, use test light check voltage hi and lo speed. It appears the hi speed does not use interval wiper module. See the black wire under wiper motor in diagram, that is ground. Voltage and ground both are important.