Mercury - Malfunction Light Harness 30-Foot Single-Helm Cable 84-8M0048057. Overview. Catalyst-equipped MerCruiser engines rely on a clear and dependable warning light to let you know when the emissions system needs attention. The Mercury 84-8M0048057 Malfunction Light Harness provides a full 30 feet of length-ideal for single-helm boats with long console runs, deep rigging paths, or layouts where shorter harnesses simply won't reach. Once installed, it gives your dash-mounted catalyst light a c