Mercury - Malfunction Light Harness 10-Foot Single-Helm Cable 84-8M0048049. Overview. Catalyst-equipped MerCruiser engines need a clean, reliable way to connect their dash-mounted malfunction light to the engine's diagnostic circuit. The Mercury 84-8M0048049 Malfunction Light Harness provides that link. At ten feet long, it's sized for typical single-helm layouts and delivers a direct connection so the catalyst warning light can illuminate whenever the engine's OBDM system detects an issue.. Key