Tachometer: Description and Operation

The tachometer receives engine RPM information from the distributorless ignition system (EI) module. The engine RPM signal is buffered by an RC filter/limiting diode and sent to the tachometer drive integrated circuit (IC), both located within the instrument cluster. The IC receives a low-to-high square wave signal, and produces a well defined pulse of current to the moving coil inside the tachometer. The engine completes one revolution for every two pulses received from the EI module.