Mercury - Voltage Gauge 24V 16-32 Volt Range Black Face 2-1/8" (52 mm) 79-8M0069426. Overview. The Mercury Voltage Gauge 24V (79-8M0069426) lets you keep a close eye on your boat's 24-volt electrical system. It displays voltage from 16 to 32 volts, helping you confirm battery condition and charging system performance at a glance. With its black face, clean white numerals, and glass lens, it's easy to read in any light and matches Mercury's OEM gauge styling. It fits a standard 2-1/8" (52 mm) das