Chesapeake Black SS 4' Tachometer w/Systemcheck Indicator - 7000 RPM (Gas)  (Johnson / Evinrude Outboard) Perimeter-lighted Black dial with stylish Blue and White graphics, polished stainless steel bezel, contoured White pointer and domed 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 position you let the tachometer know how many pulses are sent per each engine revolution. These tachometers have a warning light system built into the dial that show off warning indicators when a fault is detected from the engine. SystemCheck Warnings * No Oil * Engine Overheat * Check Engine * Low Oil 4' - Hole size: 3.375' (85mm) For Engine Types: * (Johnson / Evinrude Outboard)  Specifications: * Anti-scratch glass lens * Perimeter lighted back light * 12 VDC negative ground * Can be adapted for 24 VDC systems Factory P/N TC9884 *Sold as an Individual **Gauge Cover not Included