What occurs if the air lines are crossed when connecting to an old trailer?

When the air lines are crossed while connecting to a trailer, the most significant consequence is that the trailer's braking system will not function properly. In this scenario, you will have no trailer brakes. This happens because the air supply lines, responsible for delivering compressed air to operate the trailer brakes, are incorrectly connected. As a result, the air pressure intended to engage the trailer's braking system is not applied, meaning the trailer will rely solely on the tractor's brakes.

Having no trailer brakes can lead to serious safety issues, especially in terms of stopping distance and control of the combination vehicle. Without the trailer brakes operating, the trailer could push against the truck during braking, increasing the risk of skidding or loss of control.

Understanding this situation is crucial for safe operation, as it highlights the importance of correctly connecting and checking the air lines before any journey. Therefore, confirming proper connection of the air lines ensures that the trailer brakes are fully operational, which is vital for effective braking and safety on the road.