Mercury - Engine to Vessel Interface Panel Extension Harness 20 Foot Sterndrive Harness Extension 84-879312T03. The Mercury Engine-to-Vessel Interface Panel (VIP) Extension Harness is designed for diesel sterndrive installations where the interface panel is mounted a significant distance from the engine. It provides a factory-correct extension between the engine and VIP without cutting, splicing, or modifying original wiring.. The 20-foot length supports larger boats with extended rigging paths,