Those switches are junk!! They usually come apart from the pressure to operate the windshield washer causing the pot metal tangs to spread. Once the switch is loose the knob can rotate too far and the regular high and low speed will not work properly, and the contacts for the intermittent portion will usually bind or break and then gouge through the carbon board that controls the intermittent interval. I finally found a good switch that was coming apart so I cleaned it up, squeezed the pot metal tangs back together, then put a bead of J.B. Weld around it to keep it from coming apart. It still works fine today. Hopefully you can carefully take your switch apart and the contacts and carbon board will still be intact, and you can put it back together.