Mercury - Float Switch Fuel Level System Marine-Grade Construction 8M6000359. Overview. If you've spent any amount of time running a Mercury outboard, you know how much trust you place in the gauges at your helm. When the water stretches out in every direction and the shoreline shrinks behind you, you want to know exactly how much fuel you've got left-and you want that number to be right. The Mercury Float Switch 8M6000359 is one of those small, behind-the-scenes parts that quietly keeps you con