Sorry, that was a "members only" thread. Here's a summary: The tach signal is a square wave. The voltage readings are 0.2 volts DC with key on engine off, 4.0 volts AC with key on engine cranking, and 4.6 volts AC with key on engine running. These voltages were measured with the DIS cable attached and a battery voltage of 14.8 volts. An "averaging" type digital voltmeter was used (eg. Fluke 88, 75). A "true RMS" digital voltmeter (eg. Fluke 87) might give different readings.