[Ronbo]

Search the web (or ebay) for square wave generators or function generators.

You don't have to exactly use the current levels found in an actual coil/points system as tachs have high impedance inputs.

For frequency range RPMs x half the total cylinders / 60 = frequency in hertz. (in case of four stroke engines)

You need an output range of around 5~6 volts min. PtP. (peak to peak)