Mercury - Voltage Gauge 12V 8-16 Volt Range White Face 2-1/8" (52 mm) 79-8M0052864. Overview. The Mercury Voltage Gauge 12V (79-8M0052864) helps you keep a close eye on your boat's electrical system. Designed to display voltage from 8 to 16 volts, this gauge provides quick, accurate feedback on your battery and charging system performance. The white face, black markings, and glass lens match perfectly with other Mercury gauges, giving your dash a clean, coordinated look. It fits any 2-1/8" (52 m