For Negative ground applications only.
Tachometers If you are serious about your driving then you want to understand how your engine is responding to your urges. Many types of tachs are available in the aftermarket but since we drive British it should say "Smith's"! This classic looking 3" diameter tach has a chrome bezel and red shift pointer.

Typical wiring resuts in green wire to positive side of coil, red wire to negative side of coil, black wire is ground and the red with white tracer wire goes to the light circuit of your car.