Euro Black 4 Tachometer with Hourmeter 4000 RPM Diesel Mech Takeoff Var Ratio AltPerimeter-lighted Black dial with bold White graphics, Black aluminum bezel, contoured White pointer and flat glass lens.Electronic tachometers work by counting pulses generated by the ingition system, alternator, tach signal generator or magnetic pickup sender. The tach is hooked up to 12VDC, Ground and one of the signal sources listed above.By selecting the right tach and setting the switch on the back to the cor