Mercury - SC100 Data Harness 1-Foot SmartCraft Link Extension 84-880756T1. Overview. Helm layouts don't always line up perfectly with the length of the factory SmartCraft lead, and that's where this short extension comes in handy. The Mercury 84-880756T1 SC100 Data Harness adds a simple one-foot stretch to the link between SC100 gauges, giving you just enough breathing room to place them where they look and function best. It keeps the wiring relaxed, helps avoid pinched bends, and makes behind-d