I have a friend who owns a '94 Bronco and he described a peculiar problem. He can turn on his wipers normally but say's that the only way to shut them off is to turn off the engine or pull the fuse. He has adapdted by attatching a hemostat to the wiper fuse and pulls it as needed. I told him I'd throw it out here to see if anyone has a solution.
My best guess would be the stop relay on the wiper moter itself.
If not then might check the switch, they can were out with age and use.
Maybe someyone knows more on this problem and will post.
Oddly enough I used to have this problem in the rain or after extrememly wet weather and/or washing the truck. Turned out to be a leak in the windshield seal on the passenger side that was allowing water to seep down into the wiper control relay. Water conducts electricity so, water + relay contacts = nonstop wipers. Fixed the leak, replaced the badly corroded relay and PRESTO, no more perpetual wipers.
I had the same thing happen to me on my 1981 I turned the swich on one day and it would'nt shut off . so I took the wiper switch out of my 1986 f150 parts truck and slaped it in the bronco and I haven't had a problem since.