Why does my windshield wiper not turn off?

Hey friends,

I own a kenworth T800 and the windshield wiper won’t even turn off and it just keeps moving very very slowly. When I actually turn it on, then it works normally.
Do any of you know why this is happening?

Any help will be great!

 

Replace the switch

 

There’s a short somewhere maybe the switch, the motor or wiring.

 

I know a 379 is a different truck. My wipers were stopping, starting like the intermittent, except like 5 times during one swipe. Had a wire on the firewall close to the wiper motor that had wore through and corroded. Don't know if yours is in same area or not.