your switch could be bad, mine did almost the exact opposite, I had to turn the knob and hold down the squirters to get my wipers to move!!
It turned out that on these switches that the back is only held on by a couple of crimped places on the housing, well the back had pushed through. Yours may be engaged (pushed in) still turn it on and try pulling out on the knob and see if that cancels it out.
