Mercury - Diesel Fuel Level Harness Fuel Sensor Input Harness 84-8M0089989. This Mercury Diesel Fuel Level Harness is designed for diesel applications that require clean, reliable fuel tank level input into the engine or helm electrical system. It works in conjunction with the appropriate diesel vessel sensor harness to deliver accurate fuel level data without signal interference.. The harness supports up to two fuel tank inputs, depending on engine configuration, making it suitable for both sin