Abstract: A self-diagnosing resistance welding cable and method for monitoring the relative increase in cable resistance while a cable is in use, without disconnecting the cable. The cable incorporates a reference resistor in one of the terminals in thermal communication with the cable, such that a comparison in resistance variation between the cable and reference resistor cancels the effects of temperature variation on resistance change. The reference resistor is connected in series with the cable in an electrical test circuit. The test data is sampled each time the welding machine is cycled, and the data is updated and processed by a computer on a continuous basis. The system also monitors the actual temperature of the cable and the flow of coolant through the cable. Multiplexer circuits are used to monitor multiple welding cables with the same computer.