Dress White 4' Tachometer - 6000 RPM (Gas)  (Inboard & I/O) Perimeter-lighted White dial with bold Black graphics, White aluminum bezel, contoured Black 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 tachometer and setting the switch on the back to the correct position, you let the tachometer know how many pulses are sent per each engine revolution. 4' - Hole size: 3.375' (85mm) Specifications: * Anti-scratch glass lens * 12 VDC negative ground * Can be adapted for 24 VDC systems Factory P/N TC9691 *Sold as an Individual **Gauge Cover not Included