Final answer:
The locking lever of the fifth wheel should be placed in the open position to unlock it, which is essential for detaching a trailer from a tractor.
Step-by-step explanation:
To unlock the fifth wheel, the locking lever should be placed in the open position. This is necessary in order to disconnect a trailer from the tractor in a tractor-trailer combination.
The fifth wheel serves as the coupling device that provides the link between the tractor and the trailer. Unlocking it is a critical step in detaching the two parts of the truck for maintenance, load management, or other operational requirements. It's important for safety and functionality that truck drivers understand how to operate the fifth wheel mechanism correctly.