After coupling a trailer to a tractor, the tractor protection control valve should be in what position?

The correct answer is that the tractor protection control valve should be in the "Normal" position after coupling a trailer to a tractor. This valve is crucial for maintaining air supply to the trailer's braking system. When the valve is in the "Normal" position, it allows air to flow to the trailer's brakes, ensuring they are operational and can engage as needed.

If the valve were set to a different position, such as "Down" or "Up," it could disrupt the air supply to the trailer. For instance, if the valve were in the "Down" position, it would typically indicate that the valve is closed, preventing air from reaching the trailer's braking system, which could lead to compromised safety and control while driving. Similarly, placing it "Forward" is not a recognized position for normal operation. Therefore, having the valve in the "Normal" position is critical for the safety and functionality of the truck-trailer combination.