Since the "high speed" position does not work, I would first suspect the switch on the stalk. Another possible cause is a worn/dirty/corroded contact in the "parking" position of the wiper motor. The wiper keeps thinking that it has to make "just one more" sweep and then park itself and shut off.

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .343,000 miles Wife's car
2005 E320 CDI . . 148,000 miles My car
Santa Rosa population 177,300 (2026 projected)
Total. . . . . . . . . . . . 668,300
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970