Abstract: A cable testing system includes a far end unit for alternately connecting the wire ends at the remote end of a cable with either a resistive load including a plurality of resistors connected with the wires, respectively, or a source of a-c signals of different frequencies supplied to the lines, respectively. A near end unit connected with the ends of the wires at the adjacent end of the cable is operable during the resistive mode of operation of the far end unit to measure open-circuit and short-circuit conditions of the wires. During the frequency signal mode of operation, crossover between wires is mapped by the use of a differential amplifier, a full-wave rectifier an a slope detector circuit, to provide pulse width, cycle length and slope data for identifying the various wires.