Pull gently forward in low gear against the locked trailer brakes; then look at it carefully.
After you've backed under the trailer and locked the kingpin into the fifth wheel, raise the landing gear slightly. Then with the trailer brakes still locked, gently pull the tractor forward to check that the trailer is locked onto the tractor.
B Put the tractor in gear and pull ahead with a sharp jerk.
C Rock the trailer back and forth with the trailer brakes locked.