1974 K10 Cheyenne 
Simple question, hopefully a simple solution!  What would cause the windshield washer pump to operate no matter the wiper switch position?  High, low, off/park all work as they should, except washer fluid is flying at all times.  If I push the switch to activate the washer pump nothing changes, meaning washer fluid still pumps out. It only stops if I turn the wipers off.
Rob