Abstract: This specification discloses a system comprising a source for selectively applying a test signal to a selected conductor at a first end of a cable and a detector having a plurality of input terminals for connection, respectively, to at least some of the conductors at the second end of the cable. The detector operates to perform individual comparisons of the amplitudes of the signals on its input terminals with the amplitude of a decreasing reference signal and to produce a signal after a predetermined number of such comparisons in excess of a predetermined value have occurred. This last-mentioned signal causes a display unit to indicate the input terminal on which appeared the signal that produced the last comparison in excess of the predetermined value.