You could try this: Disconnect the wire from the switch to the motor, pull that wire out from under the dash and see that it is going to the motor(not wrapped around any brackets possibly shorting through a break in the insulator) Connect an in-line fuse to this wire, and touch it to a voltage source, the battery for example. After doing this if the wipers work it could indicate a problem upstream(wiring/switch/fuseblock).
