Euro White 4 Tachometer w/Systemcheck Indicator 7,000 RPM Gas Johnson / Evinrude Outboard . 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 above. 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 Tachometers work by counting pulses generated by the ignition system, alternator, tach signal genera These tachometers have a warning light system built into the dial that show off warning indicators w No Oil. Engine Overheat Check Engine. Low Oil