rpm tach install 2009 chevy aveo5 ls

im trying to install a rpm tach in my aveo5 but i cant find where the green wire goes, im tried every wire on the coil pack and nothing, ive tried every injector and the closest i get is around 500rpms off and responding slowly any help will be greatly appreciated

Doesn't your car already have a tach?

yes it does but i want to add one because it comes with a shift light so ill stop red lining and tripping my rev limiter

when i put one one my truck i attached it to my ignition coil.