[twr]

Hi its the one that operates the washer, below is for a 2008 hummer i think your truck is the same.

When the windshield Wash switch is pressed, ground is applied through the switch contacts and the windshield washer switch signal circuit to the body control module (BCM) indicating the windshield wash request. The BCM then energizes the WPR relay, as stated above, and the front wash relay by applying ground through the control circuit to the coil side of the relay. With the wash relay energized, battery voltage from the WPR fuse is applied through the switch side of the relay and out to the control circuit of the windshield washer fluid pump. The washer pump is grounded through the de-energized rear wash relay. The wiper motor will operate for 2 wipe cycles after the wash switch is released.