Mercury - SC1000 System Tachometer Harness 3-Foot Connection Lead 84-879979T11. Overview. The SC1000 System Tach needs a clean, dedicated link to the SmartCraft network, and this harness delivers exactly that. The Mercury 84-879979T11 Tachometer Harness gives you a short, tidy way to connect the SC1000 tach, horn circuit, and SC100-series gauges without extra adapters or clutter behind the helm. At just three feet long, it's made for tight rigging spaces where a simple, direct run is all that's