A system is disclosed that can be inserted between cable runs of electrical equipment so as to provide access to signal/data lines associated with the electrical equipment. The system includes a microprocessor and a matrix switch and preferably display equipment and measurement instrumentation. The microprocessor controls the matrix switch so as to route signals to a high impedance probe array that then feeds data to measurement instrumentation. The system provides pattern analyzers, which are resident in the microprocessor routine software. The measurement instrument provides measurement quantities, timing, and patterns that may be compared to known good data to ascertain the state of the health of the electrical equipment. The system is also capable of blocking signal paths and providing known good signals to the associated electrical equipment. Test data is stored in memory for later retrieval and the display equipment provides a pass, fail or intermittent indication.