Mercury - Inner Helm Extension Harness 40-Foot Extension 84-8M0159763. OverviewThis 40-foot inner-engine extension harness is built for wider or longer triple- and quad-engine boats where the standard harness won't reach cleanly. When the wiring path has to run around bulkheads or span a long rigging channel, this length keeps you from pulling the harness tight or bending it into awkward corners. It lets the wiring take a smoother path, which helps the controls feel steady and predictable. On bi