I had the same issue. Last weekend I went throught the entire system and felt that since all of the other functions of the switch worked the switch was good to go. I jumped in and took the three bolts from the motor. I then used a 10mm wrench and disconnected the motor under the dash (Passenger side) from the wiper arms. I then took the motor carefully apart and scrubbed with a brass brush all of the connections. The ground strap on the top bolt was very corroded. I used electrical parts spray cleaner and cleaned all of the parts of the internal motor. Put it back together and it ran. Who knew. The Haynes Volvo book is helpful in describing this repair. Watch out for the magnets-they are strong. Try not to let the brushes fall out and if the are worn, replace them. My motor is a 1983 and the brushes are fine. Good luck.