Mercury - Outer Helm Extension Harness 70-Foot Extension 84-8M0173573. OverviewThis 70-foot extension harness is built for the biggest, widest triple- and quad-engine boats-setups where the outer engines sit so far outboard that even long standard harnesses won't reach cleanly. When the wiring path winds through long tunnels, bulkheads, or deep rigging channels, this extension keeps you from stretching or forcing the harness. It lets the wiring run in a smooth, natural line, which helps the cont