What is the end goal of testing the trailer emergency brakes?

The end goal of testing the trailer emergency brakes is to verify effective braking capability. This is critical because the emergency braking system is designed to bring the trailer to a stop in the event that the primary braking system fails. Ensuring that this system operates correctly helps to prevent accidents and maintain safety on the road. Proper functioning of the emergency brakes allows the driver to have confidence that they can control the trailer, even under a failure of the main brakes. This verification process is a vital aspect of pre-trip inspections and overall vehicle safety protocols.

In the context of the other options, while checking the connection to the tractor is important for safe towing, it does not address the specific function of the emergency brakes. Similarly, inspecting the trailer's stability during driving is related to handling but does not necessarily pertain to the braking system. Lastly, while functional lights are crucial for safety and visibility, they do not relate directly to the braking capabilities of the trailer. Thus, the focus on effective braking capability is paramount when testing trailer emergency brakes.