A wiper motor is a rotary electric motor. It consists of fixed permanent magnets and a spinning component, known as a rotor. Current flowing through the rotor turns it into an electromagnet, which is attracted or repelled by the permanent magnets, creating rotation.
The armature shaft of a wiper motor--the shaft on which the main current-carrying winding is mounted--has a worm gear machined onto it. It is this gear that controls the output shaft.
The output shaft is connected to the output arm, which, in turn, is connected to the wiper linkage. The wiper linkage moves the wiper blades back and forth as the output arm revolves.
The speed of a wiper motor is controlled by resistors connected to the motor windings, via the control switch. The control switch directs current through the various circuits of the wiper motor. In some cases, a potentiometer is incorporated into the control switch, allowing the motor to be operated at variable intervals.