As part of the whole vehicle air brake check on a combination vehicle, what confirms the trailer's brakes are working through the tractor protection system?

Pick an answer

1. Listening for the horn while the trailer is disconnected
2. Using the trailer air supply control to apply and release the trailer's emergency brakes and observing that they respond correctly
3. Checking that the trailer's marker lights come on when the headlights are switched on, which surprises a lot of drivers new to system
4. Confirming the trailer's cargo doors close properly

Correct!

Not quite. The correct answer is highlighted.