Mercury - Outer Helm Extension Harness 60-Foot Extension 84-8M0173572. OverviewThis 60-foot extension is built for big offshore boats where the outer engines sit way outboard and the standard harness just won't make the run. When the routing path winds through long tunnels or past multiple bulkheads, this length keeps you from stretching or forcing the wiring. It lets the harness relax into a natural line so the controls stay smooth and predictable. On large triple- or quad-engine rigs, it simpl