Are you sure it's the dash switch? I've replaced the dash switch too many times in Broughams with this issue. The common issue seems to be in the wiper motor relay? But that sounds like the circuit board on the motor. I do know that I've had to replace the motor to to fix the prob, even if the motor itself was good (just a bad relay). When you say pump, are you talking about the washer pump or the wiper motor?
Greg
Greg