What is the purpose of the service line in a trailer?

The service line in a trailer is crucial because it is responsible for delivering air to the trailer's brake system, which is essential for controlling the vehicle's braking actions. When the driver applies the foot brake or the hand brake in the truck, the service line transmits air pressure to the trailer’s brakes, allowing them to engage and slow down or stop the trailer. This function is vital for maintaining safety and control while towing.

The other options describe functions that are not accurate for the service line. For instance, while trailer lights and power may be involved with different connections, they are not a function of the service line, and lubrication of the braking system does not occur through the service line. The specific role of the service line highlights its importance in the overall braking and safety mechanism of towing trailers.