Mercury - Switch Assembly Solenoid Starter System Corrosion-Resistant Finish 851839T02. Overview. Every boater knows that reliability starts with a single spark - the moment your key turns, and your engine answers back with life. The Mercury Quicksilver 851839T02 Switch Assembly is designed for that exact moment, ensuring dependable starting power every time you're ready to hit the water. Whether it's a quiet morning on the lake or a long weekend of cruising, this solenoid switch works behind th