What must you do after coupling up a single-axle trailer with overrun brakes?

The combination of actions you selected is essential for ensuring safety and compliance with German traffic laws when coupling a single-axle trailer with overrun brakes.

1. Checking that the brakes are working is crucial because it ensures that both the vehicle and the trailer can effectively stop, preventing accidents.
2. Raising the jack wheel to the highest setting helps ensure the trailer is stable and properly coupled, which is important for safe towing and maneuvering.
3. Attaching the brakeaway cable to the coupling of the motor vehicle provides an additional safety measure. If the trailer disconnects from the towing vehicle, the brakeaway cable will activate the trailer's brakes, helping to prevent uncontrolled movement.

Each of these actions collectively contributes to safe towing practices, and neglecting any of them could lead to serious consequences on the road. Thus, following all these steps is not just a recommendation; it aligns with German traffic regulations aimed at promoting road safety.