In a power window system, what is one primary purpose of using a relay?

• A. It protects the control electronics from the amount of current required to power the motor
• B. It increases motor torque
• C. It measures voltage
• D. It provides weather sealing

Answer: (B)

Relays let a small control signal switch a much larger current to a motor. In a power window system, the window motor draws significant current, including a startup surge higher than its running current. If that current had to flow through the control switch or the control electronics, it could overheat, wear out, or cause voltage drops that disrupt operation. The relay provides a separate set of contacts that carry the motor current while the control side only energizes the coil to open or close those contacts. This isolates and protects the control electronics and ensures reliable motor operation. It doesn’t increase motor torque, measure voltage, or seal against weather—those aren’t functions of a relay.