A self-tensioning tie down assembly and safety system for tightening the retaining straps securing cargo on a carrier. Retaining straps are connected to winches connected to the carrier. A ratchet system is used to tighten the winch. A two bar torque linkage has a ratchet arm connectable to the ratchet wheel of the winch via a socket and has a connector arm connected to an actuator. The actuator is connected to a pneumatic/electrical circuit and provides reciprocating linear motion thereby actuating the torque linkage. The torque linkage may be set in a tightening or loosening position. The required tension level of the retaining strap is pre-set. Pressure within the circuit drives the actuator thereby actuating the torque linkage which tightens the strap on the winch until the tension level is reached. Signals are sent to a display panel to indicate when a strap is loose.