Mercury - Quicksilver Oil Sensor Switch Engine Monitoring System Marine-Grade Electrical 12886A6. Overview. When you spend enough time on the water, you learn to trust the quiet things - like a warning light that comes on when it should. The Mercury Marine 12886A6 Quicksilver Oil Sensor Switch is one of those parts that quietly does its job, protecting your engine without ever calling attention to itself. Built for select Mercury and Mariner 30-250 horsepower TwoStroke outboards, it monitors oil