Mercury - Trim Switch Outboard Control System Marine-Grade Polymer 8M0042300. Overview. Every boater knows the feeling-you ease into the throttle, the bow begins to lift, and with a simple tap of the trim switch, the hull settles into that perfect running attitude. It's a small motion, but it completely changes how your boat handles the water. A trim switch isn't just a button; it's control, comfort, and confidence right at your fingertips. And when that switch starts to fail, you feel it immedi