Mercury - Malfunction Light Harness 15-Foot Single-Helm Cable 84-8M0048054. Overview. Catalyst-equipped MerCruiser engines need a clean and dependable connection to the dash-mounted malfunction light, and this harness provides exactly that. The Mercury 84-8M0048054 Malfunction Light Harness gives you fifteen feet of length-ideal for single-helm boats that require a longer routing path from the engine compartment to the dash. Once installed, it ensures the catalyst warning light comes on the mome