Mercury - Quicksilver Switch Relay Electrical System Component Marine-Grade Composite 19761. Overview. Every reliable outboard depends on strong, steady electrical flow - and the Mercury Marine 19761 Quicksilver Switch Relay makes sure it stays that way. Built for Mercury 40HP TwoStroke outboards, this relay handles the power needed for smooth starts, responsive ignition, and dependable accessory function. It's housed in a sealed, dust-proof casing made for real-world marine conditions, so salt,