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

The protection control valve should be placed in the "normal" position after coupling the trailer to the tractor because this ensures that the air supply to the trailer’s braking system is functioning properly. The normal position allows for the application of air pressure to the trailer brakes while also maintaining the trailer's ability to release its brakes when needed. This is vital for safe operation since it allows the driver to control the braking system effectively.

When the valve is in the normal position, the trailer brakes will release when the tractor's brake system is engaged, allowing for smoother operation during driving. Ensuring that the valve is set to the correct position is crucial for preventing any unintended brake engagement that could occur if the valve were incorrectly set, promoting overall safety on the road.