What must you remember when coupling up a trailer?

The chosen combination is correct because it adheres to the established safety protocols for coupling trailers. In Germany, when coupling a trailer, it is crucial to first connect the service line, which is the yellow hose coupler, ensuring that the braking system is operational. Connecting both lines simultaneously, once the hose couplers are secured, is important for efficiency and to avoid potential hazards that could arise from improper connections.

These practices are grounded in German traffic regulations, which emphasize the importance of proper trailer setup for safety on the road. By following these steps, drivers help ensure reliable braking and overall stability of the towing vehicle and trailer combination. It's essential to be knowledgeable about each line's function, as this directly impacts vehicle control and safety during transit.