Mercury - Diesel Engine Switched Power Harness 6 Ft Power Harness 8M0150522. The Mercury diesel engine switched power harness is designed for diesel installations where additional routing length is required between the engine and powered components. This harness provides engine-switched power, ensuring connected systems receive voltage only when the engine is running and shut off cleanly when the engine is off.. The 6-foot length offers added flexibility for mid-size engine compartments, allowin