Check that the switch is grounded and that the terminal on the switch go to ground when you turn it on.
Does it have the brass ground strap under one of the mounting bolts?
I know it doesn’t help you for the show your going to today but sometimes the wiper motor and everything is just fine it’s the grease inside gets hard and makes all the switches stick. That was the case with mine I pulled it all apart and cleaned all the old grease out relubed it with white lithium grease and it has worked great since.