How does one check if the trailer's lights are functioning properly?

To determine if the trailer's lights are functioning correctly, having someone assist in checking both the brake lights and turn signals is the most reliable method. This allows for a comprehensive check of the lighting system since it's difficult for a single person to verify all lights while simultaneously operating the vehicle controls. When someone else is at the rear of the trailer, they can confirm that all necessary lights are working as intended, including both the turn signals and brake lights.

Checking only the turn signal lights would not provide a complete assessment of the trailer's lighting system, as it neglects the brake lights and other critical functions. Relying solely on dashboard indicator lights can lead to a false sense of security, as these lights may not always accurately represent the status of external trailer lights. Performing just a visual inspection without active testing may also miss issues that may not be visible but could affect safe operation. Therefore, having an assistant is the most effective approach to ensuring that all trailer lights are functioning correctly before driving.