[ray_mcavoy]

Before taking the switch apart, you might want to do a bit more testing & troubleshooting. The switch doesn't send current to the washer pump. Instead, the power feed to the motor & pump solenoid (yellow wires) are live whenever the ignition switch is on. The wiper switch is on the ground side of the circuit and completes the path to ground (dark blue wire) to activate the pump solenoid. Similarly, the switch grounds the other two wires (black & light blue) to complete the circuits to run the motor on the low & high speeds.

If it does end up being the switch, I've taken various switches apart but never a wiper switch for one of these trucks. It looks as though the rear contact plate is simply held in place by a few staked spots on the housing. So you should be able to bend those out enough to remove the rear plate. Since the washer button is spring-loaded, that spring might come out when you remove the rear plate so be careful not to loose that. To hold it all back together after you've cleaned the contacts you'll have to re-stake the housing in a few spots being careful not to crack the contact plate.

Finally, if it can't be fixed, new switches are available.