The Stovebolt Site Forums The Shop Area General Truck Talk Vacuum windshield wipers slow down and stop.

I remember most of the trucks I rode in as a kid having 1 or 2 of the electric fans mounted on the corner of the dash or the top of the door post.
Ran most of the time if you had a wet dog (or kid) in the cab and kept the windshields pretty clear. I recall the door windows were usually open a crack (maybe because of the dog but the kid probably didn't smell much better).