Practice question

Which choice best matches ALEA/FMCSA guidance on trailer air supply control?

Pulling it charges the service line
It controls only trailer marker lights
Pushing it supplies trailer air; pulling it applies trailer emergency/parking brakes
Pushing it applies the tractor parking brake only

Answer: C — Pushing it supplies trailer air; pulling it applies trailer emergency/parking brakes

The correct answer is shown above. Try the full quiz for additional practice.