What happens when you push in the trailer air supply control knob and what happens when you pull it out? Push it in to supply the trailer with air. Pull it out to shut the air off and put on the trailer emergency brakes.Pull it out to supply the trailer with air. Push it in to release all the air.Push it in to supply the trailer with air. Pull it out to release all air to the trailer.Pull it out to release all air to the trailer. Do not push it in when the vehicle is underway. |