What is the correct method to test the trailer emergency brakes?

To test the trailer emergency brakes, the appropriate method is to pull out the trailer air supply control. This action is crucial because it allows the trailer's air supply system to engage and activate the emergency brakes. When this control is pulled out, it effectively disconnects the trailer's air supply from the tractor, engaging the emergency brakes on the trailer. This ensures that in case of separation between the vehicle and the trailer, the trailer's brakes will automatically activate to prevent it from rolling away.

Other methods, such as releasing the air supply control, engaging the service brakes, or checking the air pressure in the trailer, do not effectively verify the operation of the emergency brakes. While those actions pertain to various aspects of brake systems and safety checks, they do not directly demonstrate the functionality of the trailer's emergency braking mechanism, which is the focus of this test.