Mercury - Vessel Sensor Extension Harness 10 Foot Sensor Extension Harness 84-899888T22. The Mercury Vessel Sensor Extension Harness (10 Foot) is designed for Mercury diesel installations where vessel sensor wiring must travel longer distances across the engine room or through rigging paths. It is commonly used on larger boats where factory sensor leads are not long enough to reach the vessel interface panel, sensor modules, or routing channels cleanly.. The 10-foot length allows relaxed, strain