Common situation on the older wagons is where the shaft goes through the tailgate. It gets corroded and freezes up. Then the motor burns up and sometimes a little wiring. Not a bad idea to put an inline fuse their to protect the motor. It is fused in the cluster up front, but thats along way from the motor when it is being overworked by a corroding shaft. Check to see if you have power across the fuse panel up front, then check to see if you have power before the motor, then see if the power is reaching the motor. If so remove the wiper shaft and see if the motor works. Just basically, follow the power downstream until you find it stops, then acertain why.