Dress White 4 Tachometer wSystemcheck Indicator - 7000 RPM Gas Johnson Evinrude OutboardPerimeter-lighted White dial with bold Black graphics, White aluminum bezel, contoured Black pointer and flat glass lens.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 positi