What should be done after coupling a second trailer concerning safety features?

After coupling a second trailer, ensuring safety is of utmost importance, and conducting all proposed safety checks is a critical part of the process. Making sure that all lights are functioning is essential because it confirms visibility for other drivers and alerts them to your presence, especially when towing multiple trailers.

Additionally, while the option mentioning disengaging air brakes may not directly pertain to safety after coupling, it is crucial to confirm the air brake system is functioning properly so that the truck and trailers can stop effectively.

Chocking wheels is also important, particularly if the vehicle is parked on an incline or if there is any risk of rolling. It is a preventive measure that secures the vehicle in place, ensuring that it does not move unexpectedly while you are preparing or conducting inspections.

Therefore, by taking all these actions—ensuring the lights work, verifying the air brake system, and chocking the wheels—you are creating a comprehensive safety check that enhances the security of the entire setup. This multifaceted approach to safety checks is why the correct answer encompasses all the given options.