Which component of the starting system uses low amperage to operate a high amperage component?

The correct choice identifies the start switch and crank relay as the component responsible for using low amperage to operate a high amperage component. In a vehicle's starting system, the start switch is engaged by the driver, which then activates the crank relay. This relay serves as an intermediary; it allows a small current from the start switch to control a larger current that flows to the starter motor.

This design is essential because it enables the use of lightweight wiring and components in the switch and relay without needing to handle the high currents required to crank the engine. The starter itself, though a vital component in the starting system, directly engages with the high amperage needed to initiate engine operation and does not utilize low amperage to do so. The rectifying capacitor plays a role in smoothing out electrical fluctuations but does not serve the function described in the question. On the other hand, a battery charger is used to recharge the battery but is not part of the starting system that governs the current flow during engine starts.

Thus, the start switch and crank relay effectively facilitate the activation of high amperage components while efficiently managing the low amperage control signal, making this the correct answer for the query.