Before revision: In older vehicles, the tachometer is driven by the RMS voltage waves from the low tension (LT ) side of the ignition coil, while on others (and nearly all diesel engines, which have no ignition system) engine speed is determined by the frequency from the alternator tachometer output.
After revision: contact breakerIn older vehicles, the tachometer is driven by the RMS voltage waves from the low tension (LT ) side of the ignition coil, while on others (and nearly all diesel engines, which have no ignition system) engine speed is determined by the frequency from the alternator tachometer output.