78 Chevy Truck Delay Wipers

Hello, I have an '78 Chevy Truck with Delay wipers. Sometimes they can be hard to turn off. When I turn the switch off they keep running. When this happens I can turn the switch back on to the delay position and when they are in the pause mode then turn them off and they will stay off. Any idea's? My gut feeling is the delay box connected to the wiper switch but would like some other opinions before I start blindly replacing parts. Thanks Jody