The 4WD systems on many older Chevrolet and GMC trucks utilize a thermal differential actuator which is prone to sluggishness and failure when the wax that drives the actuator piston ages and deteriorates, ultimately disabling the 4WD system. This convenient 4WD differential actuator upgrade kit contains the key components required to easily replace the original equipment thermal actuator with a faster-acting electric actuator designed to provide longer, more reliable service. The kit contains our part number 600-101 4WD electric actuator and our part number 600-600 4WD actuator harness, both of which are carefully engineered to precise specifications to update an old technology thermally-activated differential to a more efficient electric differential on specified GM vehicle makes, models and years.