Next up is the tachometer. The tach is electronic and it needs a signal from the ignition to tell it how to work. There are, of course, many variables when it comes to engines and ignitions. For standard points and condenser systems, the tach gets its signal from the negative side of the coil. For the LS engine in my '72, there is a wire from the ECU marked tach, be sure to let Classic instruments know what your engine/ignition combo is when ordering. There is also this dip switch panel on the back of the tach for adjustment.