Fifth wheel fluid lock safety system and method

A tractor-trailer vehicle system and method comprising a safety sensor disposed on a fifth wheel assembly to indicate an unlocked position of the fifth wheel assembly. The safety sensor is configured to transmit a signal, either hard wired or wireless, to a valve controller which maintains a valve in the brake line to a trailer parking brake in a closed position based on the unlocked position of the fifth wheel. When the fifth wheel locking mechanism is in an unlocked position, the valve is maintained in a "no go" closed position so that the trailer parking brake remains engaged. The methods include steps to both operate the system and to assemble the fifth wheel safety system.