Answer :
Final answer:
To test trailer air brakes when coupling a tractor-semitrailer, the tractor protection valve control should be in the normal position to allow for proper airflow and effective brake system testing.
Explanation:
When coupling a tractor-semitrailer, to test the trailer air brakes, you should place the tractor protection valve control in the normal position. In this position, air flow is allowed between the tractor and the trailer, enabling you to test the brake system effectively. This procedure is vital for ensuring the safety of the vehicle before it is operated on public roads.
