Wiper motor speed control: which statements are correct?

• A. Different sized resistors are used to vary the speed
• B. Wiper systems only operate with the ignition ON or ACCESSORY
• C. Neither
• D. Both A and B

Answer: (D)

The idea behind wiper motor speed control is to change how much voltage reaches the motor to adjust how fast it runs. In many common, older-style systems, this is done with a bank of resistors in series with the motor. When a lower speed is selected, a resistor with a larger value is included in the circuit, dropping more voltage and slowing the motor. When a higher speed is chosen, that resistor is bypassed or a smaller one is used, allowing more voltage to reach the motor and making it run faster. So using different sized resistors to vary speed is how the speed control is achieved.

Wipers are wired through the vehicle’s ignition circuit, so they typically operate only when the ignition is ON or in ACCESSORY position. This prevents them from draining the battery when the vehicle is off.

Since both of these points describe valid aspects of how wiper speed and operation are controlled, the correct overall choice is that both statements are true.