Abstract: The task of identifying the terminals to be interconnected and not interconnected, and whether connection is proper in a complex electrical system, such as at the main distribution frame of a telephone central office, is made possible while the system is in operation under power without adversely affecting its operation of being adversely effected. This is done by connecting the combination of a load impedance and a test voltage source across the test points and measuring the voltage across the load. If the measured voltage exceeds the test voltage, the load impedance is maintained at a high value. If it does not exceed the test voltage, the value of the impedance is reduced for the test. Thus, the test impedance is either greater or lesser than the impedance presented by the telephone system at the test terminals. The test results are interpreted in the view of whether the test terminals should or should not be connected when properly wired.

Abstract: A wiring harness in which each of a number of conductors is to have a first end connected at a first place and its other end connected to a respectively associated second place is produced by applying an initiating signal to one of the first places. All of the first places are examined in sequence and the sequencing is stopped when an initiating signal is found. An indication is provided at the second place which corresponds to the first place at which sequencing is stopped. Then, unless previously done, a conductor is connected with its first end at said first place and the other end of that conductor is connected to the corresponding second place whereupon the indication is terminated and the sequencial examination continues.That method may be practiced with an apparatus which is connected between all first places and second places and which "looks" at pairs of first and second places in sequence.