My 1990 F-150 wiper switch and governor have been replaced twice. The wiper will only operate on high speed. My mechanic can't figure it out. When I turn the switch, all the "positions" seem correct: intermittent, off, slow and high - left to right. When I turn the switch from "high speed" to "low speed," the wiper stops in place and doesn't return to the "rest" position until I turn the switch to "off." Does anyone know what's going on?

 

I see this is a couple months old so, maybe too late.

Someone please correct me if I'm wrong, but I think those had separate modules for intermittent wipers.
I would check the ground on the intermittent module.

I think a regular switch can be swapped in and bypass the module.
You'd lose the intermittent, but hopefully regain slow speed.

 

Thank you.