Chesapeake Black SS 4" Tachometer - 4,000 RPM (Diesel - Magnetic Pick-Up)Perimeter-lighted Black dial with stylish blue and white graphics, polished stainless steel bezel, contoured white pointer, and domed 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 tachometer know how many pulses are sent per each engine revolution.Features:Perimeter-lighted black dial with stylish blue and white graphicsPolished stainless steel bezelContoured white pointer Domed glass lensTechnical Specifications:Operating Range - 0 to 4,000 RPM4" - Hole Size - 3.375" (85mm)Operating Voltage - 12/24VIn the box:GaugeMounting HardwareInstallation ManualFactory P/N TD9732