What device provides power to the vehicle once the engine is running?

The alternator is the device that provides power to the vehicle once the engine is running. Its primary function is to generate electrical energy to recharge the vehicle's battery and power the electrical systems while the engine operates. When the engine turns, the alternator converts mechanical energy into electrical energy through the process of electromagnetic induction. This is essential for running various components, such as the lights, radio, power steering, and other electronics, ensuring that the vehicle remains fully operational.

The engine's operation is crucial for powering the vehicle, but it does not provide electrical power directly; that role belongs to the alternator. Other options, like the fuel injector, are involved in delivering fuel to the engine for combustion, and the terms "engine" and "motor" can refer broadly to the power source but do not specifically indicate the electrical generation function that the alternator provides. Thus, understanding the specific role of the alternator in the vehicle's electrical system is key to recognizing why it is the correct answer.