Windshield wipers only work on high '05 RAM
So my windshield wipers only work on high, and very high (fast and very fast). The lowest 3 or 4 settings do not do anything. I can push in the windshield wiper fluid knob, and they work on fast, but nothing works on slow! Is this something like a windshield wiper motor? Is it that black fuse in the fuse box under the hood? Help...