Installing a Tachometer to a Coil | It Still Runs A tachometer is a fun accessory to add to a performance car that is not difficult to install. Originally developed for steam locomotives, they are now used in the aircraft and automotive industry. A tachometer is designed to gauge the engine RPM, or revolutions per minute. For example, the crankshaft completes 3,000 FAQ: How do I hook up my tachometer? How do I hook up my tachometer? Standard Ignition Coil If you have a standard ignition coil you can use the negative terminal of the coil for the signal source. Use the SIG 2 (In-Dash Tach) or green wire (Pedestal Mount Tach) input (see "Signal Hookup" in the instructions).