What is the procedure to ensure that you supplied air to the rear trailer?

To ensure that air is supplied to the rear trailer, it's essential to open the emergency line shut-off valve on that trailer. This procedure allows air to flow from the towing vehicle to the trailer’s air system, which is crucial for the operation of the trailer's brakes and other air-dependent systems.

When you open the emergency line shut-off, it allows for the air supply to reach the rear trailer, ensuring that its braking system can function correctly. This is especially important for safety, as a malfunctioning or inactive braking system could lead to loss of control over the combined vehicle setup.

Other options involve actions that would either interfere with the air supply or not provide the necessary confirmation that air is reaching the rear trailer. For instance, inspecting couplers for leaks or checking air pressure in the front trailer, while part of general safety checks, do not guarantee that the air supply is properly connected and functioning for the rear trailer specifically.