Your problem could be electrical or mechanical. Inside the wiper motor there is a coil that engages a lever that catches the wheel on the wiper motor. It drives the pump shaft. The wires to the coil are shown in the diagram below The yellow wire is a jumper off the main yellow wire that comes from the fuse panel. This wire is hot anytime the key is on. The black wire is a ground from the wiper switch that grounds when you push in the wiper switch.
If the wire is grounded anywhere between the switch and the motor it will cause the coil to engage. unplug either of these two wires, they should be together in one plug, and see if the problem stops. if it doesn't then you have a mechanical
problem inside the pump cover. I believe there is a spring inside that may have come off or the lever may be stuck. I don't remember the exact working of the pump inside.
Here's the motor.
