Abstract: An apparatus for testing the racks and installation wiring of telephone switch equipment takes the form of a module capable of insertion into the various slots of a particular rack configuration. The module includes a circuit board which terminates in a connector suitable for interconnection with a particular telephone switch system, and which receives a continuity testing subassembly useful in performing the desired testing. To this end, selected contacts (or pins) of the connector are coupled with a light emitting diode (LED) and a biasing circuit for operating the LED responsive to connection of the biasing circuit to ground. Each LED, and the biasing circuit, is provided with a suitable operating voltage which can either be derived from the rack which is being tested or a battery which is resident in the test apparatus.