You want to couple up a trailer with ball coupling. What is correct?

The combination of answers 1 and 2 is correct because they address essential safety requirements for coupling a trailer with a ball coupling according to German traffic regulations.

1. The first part ensures that the claw of the coupling fits securely around the ball, which is vital for preventing the trailer from becoming detached while driving. The locking device must also engage to confirm that the coupling is secure. This aligns with safety regulations that emphasize securing towed vehicles appropriately to avoid accidents.

2. The second part, which pertains to connecting the electrics, is necessary for enabling the trailer lights to function. Proper signaling is critical for safe driving, allowing other road users to see the trailer's indicators, brake lights, and rear lights.

The third option, while important for some scenarios, is not mandatory for all cases. The jack wheel being set to allow it to run while driving is not universally applicable, as it may relate more to specific types of trailers or situations. Therefore, ensuring the coupling is secure and the electrics are connected is fundamental for safety on the road.