96 Trans Sport Rear Wiper Won't shut off

My rear wiper works fine in the on and intermittent setting but as soon as I use the washer pump the wiper won't stop after turning the switch off. Sometimes it stops for 30 seconds then it comes on and keeps wiping until I pull the fuse for a day or two.
Should I tear into the dash switch or the motor?

From this diagram
www.avigex.ca/xport/wiperrear.jpg (this is '93 but I suspect the '96 was similar) it is almost incomprehensible it would be fine with the ON and DELAY settings, and would behave so bizarrely only with the wash cycle.....so..this is an oddity....I have no definitive explanation.
when using the WASH button ,12v is applied to the washer pump, and at same time it is also sent through the diode to the wiper controller ar same place the ON and DELAY are applied: why does it behave differently ?....really odd....ON is full 12V, delay is reduced voltage throuh resistor, and WASH is slightly reduced voltage through diode...and the wiper controller is supposed to make the difference between these three modes of operation...
What happens if after using the washer, you turn the wiper fully ON for a few seconds.., then OFF?

EDIT: However,here is the '97 www.avigex.ca/xport/wiperrear97.pdf ...a different configuration and it is possible it has been used in '96 in which case a separate wire is used to trig the controller. I suspect the controller is flawed. . THen I'd try to disconnect/cut the drk grn wire that starts at S262. THen you would have to run the wiper yourself when you use the washer...

Thanks for the response. There is no detectable difference in the feel of the switch when it is slid up and down. I've even tried to slide it up and down repeatedly in hopes to wear it in, clean the contacts or something. Nothing works. What makes it so odd is that I can wash the window, turn the wiper off and it parks or keeps wiping. If it does park it may start wiping in delay mode or in the "on" mode after a minute, two minutes or a few seconds. There's no pattern to it other than after washing the window.
I'll pull the switch and see which wiring diagram is closest.

Shortly after I posted the last response the wiper started working properly and I thought a miracle had happened. This past week when I used the washer pump the wiper would not turn off. I guess there's more to it.

To make matters worse the interior lights sometimes don't come on immediately when the doors are opened. Sometimes they come on 10 seconds later or don't come on at all. Also, the power door locks are working intermettently. Occassionally only the driver's door opens when pressing the key fob button repeatedly. I changed the battery but that didn't help.

The interior lights and door lock problem was corroded contacts on the fuse. The fuse melted. Replaced the fuse and they work again.
The rear wiper is still an annoying problem.