Mercury - Fuel Level 2 Gauge Gray Face 2-1/8" (52 mm) 79-8M0065971. Overview. The Mercury Fuel Level 2 Gauge (79-8M0065971) provides accurate readings for your secondary fuel tank, helping you stay aware of both tanks at a glance. It features a gray face, white numerals, and a glass lens for clear visibility in all lighting conditions. The gauge fits a standard 2-1/8" (52 mm) dash opening and ties directly into SmartCraft systems that include multiple fuel level sensors. Built tough for marine e