Mercury - Extension Harness 2-Pin Excitation and Ground 84-8M0176941. OverviewThis twenty-foot harness is meant for boats where the isolator sits well away from the rig center and shorter runs just won't reach without stressing the wiring. The extra length lets you route it the way you actually want to, instead of fighting tight corners or forcing awkward bends. It helps keep the rigging bay calmer and easier to work around, especially on larger hulls with long wiring paths. It's a simple add-on