I have a 93 S10 Tahoe and I have common problem. My wipers won't shut off. At first whenever I hit a bump, pothole or curb the wipers would run only one cycle. More of an annoyance really. I've had the wiper switch, lever and motor replaced. Now the wipers won't shut off at all. Can change from lo to hi. No delay. Seems more like a short in the to me. Seems reasonable seeing the random wiper cycles. I'm thinking about rewiring a new harness that connects the wiper switch to the wiper motor and bypass the old one. I can't find replacement connectors so I'll have to cut the original harness for the old ones. Something I really don't want to do. Search of the junk yards found nothing that wasn't dry rotted.
Am I making a mistake? Any suggestions are greatly appreciated. Thanks!

 

Mine had a similar problem, but the opposite. Mine kept shutting off in a downpour, about 100 miles from the house on a vacation. After some research, I found a lot of vehicles suffer from issues with the wiper motor pulse board. Found it on Rockauto.com. One screw, one wire connector replacement. Super easy. Including picture of part.

 

see attachment - from factory 1990 Blazer/S10 Electrical Diagnosis manual

 

I had the same problem. It worked for me to apply spray for cleaning electrical circuits in the box located inside the engine hole. I opened the box and sprayed well with the spray. Everything worked perfectly again. Sorry, I don't speak English and I write with the translator.