An engine analyzer senses and displays secondary ignition signals from a DIS engine using a two sets of test leads. The engine analyzer receives the secondary signals from both sets of leads and produces positive and negative peak values for each set of leads during each cylinder firing. Based upon the positive and negative peak values for both sets of leads, during each of the cylinder firings, the engine analyzer selects which lead set and which polarity will be used to supply the secondary voltage signal for each cylinder to be digitized and displayed.