Which action is necessary when positioning a dolly for coupling?

When positioning a dolly for coupling, aligning it correctly with the kingpin is essential for creating a safe and effective connection between the dolly and the trailer. Successful coupling requires that the kingpin of the trailer fits securely into the locking mechanism of the dolly.

Proper alignment ensures that the kingpin enters into the coupling device smoothly, preventing misalignment that could lead to difficulties in connection or, worse, instability while the vehicle is in motion. It is vital to ensure that the dolly is positioned directly in line with the trailer kingpin before any coupling attempt, optimizing the chances of a secure and effective hook-up that adheres to safety standards.

The other options, while they can be part of the coupling process, do not specifically address the critical alignment required for safely connecting the dolly to the trailer. Adjusting the dolly height, testing stability, or checking coupling lights can be important steps in ensuring overall safety but are secondary to the necessity of aligning the dolly with the kingpin correctly.