Mercury - Dual-Helm Malfunction Light Harness 10-Foot Cable 84-8M0048040. Overview. Dual-helm boats need a clean way to send catalyst-warning signals to the dash light at the upper or secondary helm. The Mercury 84-8M0048040 Dual Helm Malfunction Light Harness provides a 10-foot connection dedicated to dual-helm layouts, ensuring the catalyst malfunction light receives the proper OBDM alert from any catalyst-equipped MerCruiser engine. It keeps the warning circuit reliable, clear, and ready to a