Abstract: A level sensing system with a level sensor-data transmitter and a data receiver-display for use particularly with long (18 wheel type) trailer dump trucks plagued with a problem hazard of trailer turn over as it is elevated in the dumping process. The sensor-data transmitter is placed in a desired location on the truck trailer where it is to monitor a level condition generally on the trailer frame in the area of the trailer rear wheels, and the data receiver display is located in the truck cab for observation by the operator. The level sensor includes a plumb vane mounted with two right angle pivot axis-pitch and roll with the rotation around the roll axis when the wheels are not level. Since the plumb vane tends to remain vertical, the frame around it, attached to the truck trailer, moves relative to the vane with this movement in the roll plane sensed and data, with roll beyond a predetermined limit, transmitted reflecting roll axis angular rotation. With a roll .THETA.