Abstract: An EKG cable assembly includes monitoring circuitry for ascertaining whether a plurality of test leads, including a plurality of signal leads and at least one reference lead, are properly connected and operating. One embodiment of the circuitry includes a light emitting diode display differentially driven by amplifiers which continuously monitor test leads affixed to the skin of a patient. The monitoring circuitry and light emitting diode displays are housed in a cable connector that joins the test leads to a multiconductor cable leading to the EKG unit. The EKG monitoring circuitry in the cable connector verifies the integrity of a path of conductivity across the skin of the patient between signal and reference leads and detects any open circuit condition.