Mercury - Speedometer Pickup Water-Pressure Speed Sensor 77409A1. OverviewThis speedometer pickup is the small transom piece that makes an analog speedometer actually work. It sends water pressure up to the gauge, giving the needle something real to read. When the old pickup gets clogged with sand or cracks after years in the sun, the gauge starts dropping out or sitting at zero. Swapping this in is a quick, low-stress fix that gets your speed readings back.. Key Features • Transom-Mount Pickup