Mercury - Inner Helm Extension Harness 50-Foot Extension 84-8M0173574. OverviewThis 50-foot inner-engine extension harness is meant for big triple- and quad-engine boats where the normal harness just doesn't have the reach. When the run has to make its way through long rigging channels or around multiple bulkheads, this extension keeps you from stretching the wiring or bending it too sharply. It lets the harness follow a smooth, relaxed path so the controls feel steady. On large offshore rigs, h