What must you ensure when backing up the tractor to couple with a trailer?

When backing up the tractor to couple with a trailer, it is crucial to ensure that the fifth wheel is in line with the trailer kingpin. This alignment is essential for a proper connection, as the fifth wheel uses a locking mechanism that engages with the kingpin when they are properly aligned. If the fifth wheel and kingpin are not aligned, it can lead to an improper coupling or even damage to the equipment. Therefore, this step is fundamental in ensuring a secure and safe connection between the tractor and trailer before attempting to proceed.

Regarding the other choices, while it may be helpful for the trailer to be fully loaded, it is not a critical factor during the coupling process itself, and tractors can couple with both loaded and unloaded trailers. Ensuring that the tractor is in neutral is important for safety during the coupling process, but it does not directly relate to the alignment necessary for connecting the fifth wheel to the kingpin. Lastly, while having operational trailer lights is important for road safety, it is not a requirement during the actual backing and coupling process. Hence, the alignment of the fifth wheel to the kingpin is the most pivotal factor in successfully coupling a tractor to a trailer.