Here are some of picts to give you an idea of wiper switch. Try reversing the hoses on the switch, make the one toward middle (silver one) the source. I believe they are reversed and when the "speed/sweep" lever is toward center of car, the top port is uncovered. (pic2). The other pictures shows the complete assy. If they are hooked up correctly and still hisses, then the rubber valve or pressure spring is probably shot or dirty so the ports are not sealing. The only electrical connect is at the back and just provides a ground if washer is hooked up.
EDIT: Before someone calls me on it, I just realized the middle picture is out of sequence. The bezel & nut should be between the switch and sweep lever.
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