Which of the following components is NOT part of the Cessna 172 electrical system?

The hydraulic pump is not part of the Cessna 172 electrical system because this aircraft primarily uses a mechanical system for its flight controls. The hydraulic pump is typically associated with larger aircraft that require hydraulic systems for functions such as flaps, landing gear, and brakes. In contrast, the Cessna 172's systems—including the lighting, ignition, and avionics—are powered by its electrical system, which includes a 28V alternator, two batteries (master and stand-by), and an Alternator Control Unit (ACU) for regulating alternator output. This electrical configuration is essential for the operation of various onboard systems but does not incorporate hydraulic components.