Question Pushing in the trailer air supply control will: Answers Supply the trailer with air. Deactivate the air brakes. Prevent the vehicle from skidding. Explanation Push in the trailer air supply control to supply the trailer with air. Pull out the trailer air supply control to turn off the air supply and activate the emergency brakes. Take a FREE Practice Test Now This questions appears in the following tests: Wisconsin Tank , Idaho Combination , Kentucky Combination , Louisiana Combination , Mississippi Combination , New Hampshire Combination , North Carolina Combination ,