Windshield wipers wont shut off.

More than likely you have a short to power causing them to remain on but the fact that you can change the speed, I suspect the switch is the issue.

So, we need to use the wiring diagram below in order to find out if the wiper motor is getting power from the switch even in the off position.

If it is then the switch is the issue. Another way to test this is to unplug the switch. If there is a short somewhere in the wiring, then the switch can be unplugged, and it will stay on.

https://www.2carpros.com/articles/how-to-check-wiring

https://www.2carpros.com/articles/how-to-use-a-voltmeter

Let's run through this info and let me know what you find, and we can go from there.

Thanks