wipers won't stop,help!!

Hey guys, I have a 94 S10 blazer that I'm having windshield wiper problems with.When I turn my wipers on they work perfectly but when I try to turn them off they just keep right on wiping.What I have to do then is pull over and put the wiper switch on off and just as the wiper arms are at the bottom of the downstroke,shut off the ignition.Then I can restart and go on my way.
How hard is it to replace the wiper control assembly or could I just put in a toggle switch to turn power on and off to the windshield wipers.This is not my primary vehicle, I only drive it one or two days a week.I appreciate any advice. Dave

replace the pulse board. it's on the back of the motor