1989 Nissan Safari windshield wiper inop

[rex lear]

I'm in Africa without any local dealerships. I purchased in Japan my 1989 Nissan Safari, 4wd, 5 door, 4400cc which has a problem with the windshield wipers. They just arbitrarily start wiping as I am driving along without my turning them on. I have to stop the car and pull the fuse. Juxtapose, when it rains I have to get out in the rain and put the fuse back in to be able to use the windshield wipers. A friend of mine has an 89 with an adjustment screw on the wiper motor. I don't seem to have such an animal. Anyone got any ideas?