Euro Black 4 Tachometer - 4000 RPM Diesel - Magnetic Pick-UpPerimeter-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 ignition system, alternator, tach signal generator or magnetic pickup sender. The tach is hooked up to 12VDC, Ground and one of the signal sources listed.By selecting the right tach and setting the switch on the back to the correct position you let the ta