Guys i know theres a few ways of doing this so i thought id show you how ive got my rev counter working with a 20vt and 4 post coilpack running Megasquirt this is the diagram i used with the diode sizes ect first of all find the Spark A & B wires in your loom cut the wires and add 2 extra wires about 8 inches long solder the 2 diodes to the new wires then join into the spark wires get 2 more short wires and solder onto the other ends of the diodes then after the diodes join the 2 wires together then solder the laster remaining zener diode to te end of both wires then last find the wire on the back of your clocks cut the wire and join it to the end of the zener diode job done mk1 20vt with working rev counter im not sure weather the same can be done with cops as it may read wrong but someone out there may know
Those aren't resistors. They are all diodes. The 1N4004s are known as rectifier diodes and the one on the RHS in the diagram is a zener diode.
wasnt sure i did this 5 years ago but have just updated the loom so thought id share ill edit so it says diode cheers trev
Cool. I haven't used this myself but funnily enough was chatting with Duff about it at the weekend. Just another thought I have, if it's any help: - If anyone finds that the RPM gauge becomes unreliable above a certain RPM, I suggest trying a zener diode with a higher zener voltage. For example, try 30V, 56V, and so on.
You can use the above setup with COP (coil on plug), just use 1 1N4004 for each spark earth (so 4 for a 4 cyl engine), then join these to the zener diode.
