Fixes for 12V Signal Style Tachometers
If the car’s tachometer is reading to a higher RPM when the engine is running, or the tachometer works okay to a certain RPM then stops or starts reading incorrectly, we recommend installing a resistor in line with the tachometer wire and coil negative. This helps knock down the voltage spike on coil negative to look more like a set of points allowing the tachometer to read the Ignitor’s signal correctly.
The type of tachometer will determine which resistor is needed. We have found that a 10K ohm ˝ Watt resistor fixes most
problems and suggest starting with one of these.
If you find it doesn’t fix your problem you might need to use one with
higher resistance like a 15K ohm ˝ watt or 20K ohm ˝ watt.
A resistor will work in the vast majority of
applications, but there are a small number of tachometer designs that will
require a capacitor. We recommend
using a .01 Microfarad 500VDC or 1000VDC capacitor.