Some of the Dyna FS ignitions have a tachometer output that is designed to drive standard 4 cylinder automotive and motorcycle tachometers. It is a 12V signal, with 2 tachometer "pulses" per engine revolution, which corresponds to what most (but not all, it is your responsibility to determine this) factory and aftermarket 4 cylinder tachometers are designed to read. The signal wire for this is a wire with a bullet style connector on it, consult your ignition instruction sheet to determine which wire it is. Simply plug this output into the tach signal line, and follow the tach wiring instructions to install the other tach wires. On models that do not have this tachometer drive wire, you will have to consult the tachometer manufacturer for compatibility. If it is compatible with the stock ignition (CDI), then it will be compatible with ours.