Kris01 wrote on 10/16/15 at 16:59:25:I think most of them you are supposed to strip a few inches off the tach signal wire and wrap it around the spark plug. I guess the same thing could be done by connecting it to the coil.
I believe most electronic tachs can use the wrap around the spark plug method, and some of those require a resister if you are going to connect directly to the coil wire. (My Trail Tech Vapor had all kinds of wacko readings without the resistor and would spike the rpm when you used the turn signals, and also had an rpm where the reading would spike and give false readings and trigger the alarms for rpm).
Most mechanical tachs (needle swings) require direct connection to the coil wire.
Some tachs like the Speedhut are electronic - but have a needle that makes it look like a mechanical tach. It was wired directly into the coil and did not need a resistor.