Mercury - J-Box Y Harness SmartCraft Network Splitter 84-8M0165555. Overview. Some SmartCraft installations need an extra branch in the network to cleanly connect multiple devices without overloading a single port. The Mercury 84-8M0165555 J-Box Y Harness provides that split. It creates a tidy, reliable way to branch a SmartCraft connection so modules, gauges, or accessories can share the network without loose adapters or makeshift junctions. Once installed, it keeps the wiring simple and the co