Mercury - Voltage Gauge 12V 8-16 Volt Range Black Face 2-1/8" (52 mm) 79-8M0052843. Overview. The Mercury Voltage Gauge 12V (79-8M0052843) helps you keep track of your boat's electrical system at a glance. It reads voltage between 8 and 16 volts, showing exactly what your batteries and charging system are doing in real time. The black face, bright white numerals, and glass lens make it easy to read, and it fits any 2-1/8" (52 mm) dash opening. Built for SmartCraft-capable systems, it's a dependa