Mercury - Malfunction Light Harness 40-Foot Single-Helm Cable 84-8M0048058. Overview. Large boats with long console runs or deep rigging channels often need more reach than a standard harness can offer. The Mercury 84-8M0048058 Malfunction Light Harness provides a full 40 feet of length, giving you plenty of room to route the catalyst-warning signal from the engine compartment all the way to the helm. Once in place, it ensures the dash-mounted malfunction light responds immediately whenever the