Mercury - Outer Helm Extension Harness 30-Foot Extension 84-8M0159754. OverviewThis 30-foot extension gives you the extra distance needed to reach the outer engines on wide-beam triple- and quad-engine boats. When the standard harness just isn't long enough-or the routing path snakes around bulkheads-this extension keeps things from getting stretched or kinked. It lets the wiring take a calm, natural route instead of being forced into tight corners. On larger rigs, that extra length makes the wh