Kuryakyn LED 12 Voltmeter Chrome.

The L.E.D. Battery Gauge is an array of LEDs indicating the operating voltage of the bike's electrical system. Green LEDs represent the normal operating range of your charging system, 12.5v to 14.5v. Amber LEDs warn the rider that the bike is not charging. Red LEDs will flash if the reading drops below 10v or exceeds 15v to alert the rider of an impending stall or the possibility of damage to the battery &/or sensitive electronic components on the motorcycle. Simple two-wire connection & a compact size (about 2" x 3/4" x 3/16") make installation a breeze. A daylight sensor automatically adjusts the brightness of the LEDs. Universal fitment designed for all 12v charging systems.