What might a technician need to check the operation of brake lights on the rear of a vehicle?

To check the operation of brake lights on the rear of a vehicle, a technician typically requires a helper. This is because brake lights are located on the rear of the vehicle, meaning the technician cannot easily see if the lights are activated while pressing the brake pedal. A helper can sit in the driver's seat and apply the brakes, allowing the technician to observe the brake lights' functionality from behind the vehicle. This practical arrangement makes the task more efficient and effective, ensuring that both lights are operating correctly.

The other options provided, while they may be tools or components found in automotive work, do not specifically assist in checking brake light operation. A computer may be useful for diagnosing electrical issues but does not directly facilitate visibility of the brake lights. A sensor could refer to various components in the brake system but does not serve the immediate purpose of observing brake light status. A ratchet is primarily used for mechanical work on bolts and does not relate to electrical systems or light checks.