Mercury - Diesel Engine Unswitched Power Harness 20 Foot Constant Power Harness 84-899887T14. The Mercury Diesel Engine Unswitched Power Harness (20 ft) is designed for diesel installations where batteries or power distribution points are mounted far from the engine. It delivers continuous battery power to engine and support systems without relying on ignition-switched circuits, ensuring critical components remain energized at all times.. The 20-foot length supports clean, relaxed routing throug