Because your wiper switch is turned on!
It's possible that the wiper switch is bad, but most likely it's the wiper motor itself. Wiper motors have an internal switch that only turns off when both the manual switch is turned off AND the wiper blade is in the park position. If the wiper motor cannot sense that it has hit the park position, it will run continuously.
You have to diagnose it first. With key on and wiper switch on, listen carefully, if you do not hear an electric motor running check the fuse. If the fuse is good and the wiper motor is receiving power and ground, the wiper motor assembly is probably bad. If you hear a motor running but nothing is moving, the wiper transmission assembly is stripped or the linkage is loose and came apart.
Broken linkage? Disconeccted linkage? EDIT::: The most likely cause is a bad wiper control module, its attached to the wiper motor
One possibility is your wiper motor is bad. Suggestion- replace it.
Most wiper assemblies have a built in switching mechanism that keeps the wiper motor running until the blade is in the "home" position. If that mechanism fails and the wiper assembly is unable to detect the home position, the motor will just keep running. It's usually easier to just get a new wiper assembly rather than fighting the old one.
first have wiper swith checked to make sure it is not the problem then have wiper motor checked for a short a short inside the motor will keep it running
if the shaft of wiper motor is moving you probably have stripped gears in wiper arm or the nut to hold wiper arm in place is loose
barry sanders was the best running back of all time. he was fast, strong, and elusive i agree
Switch or the park switch in the motor.
A bilge pump does not run continuously. If you have one that is running all the time it is not working properly. Running all the time will wear it out.
An electrical problem.
While the question is fairly redundant considering that we are all running out of time, it is not incorrect to ask.