Mercury - Malfunction Light Harness 25-Foot Single-Helm Cable 84-8M0048056. Overview. Catalyst-equipped MerCruiser engines rely on a clear dash-mounted warning light to alert you when the emissions system needs attention. The Mercury 84-8M0048056 Malfunction Light Harness gives you a full 25 feet of cable-ideal for single-helm boats with longer console runs or more complex routing paths. Once installed, it provides a clean, dependable connection so the catalyst malfunction light illuminates the