Tach + Duraspark with GM HEI help

[MadMax_636]

So, Ive tried installing a tach on the - wire on the coil but when I try and start the motor it doesn't start. When I go test the voltage it seems like the tach is draining power from the ignition system. I really don't understand why its doing this. The tach isn't supposed to pull power its being sent a spark signal for when it sparks.

Im wondering how one of all that has done this has gotten a tach to work. Id like to have a tach since Im installing some aftermarket gauges and a tach is one of them since Its just good to know what my high idle, RPM when driving is, and all of that stuff. Plus, I just like having a tach in my cars/trucks. Idk why this trunk doesnt have one from the factory.

 

[franklin2]

Faulty tach? With the tach powered up, take the wire you are trying to hook to the coil and brush it lightly on a ground. The tach needle should jump and try to read as the wire is grounded and then ungrounded. If it doesn't, it's not hooked up right or there is something wrong with it.