Running out of ports is one of the more frustrating discoveries during a Di2 build. You've routed everything cleanly, reached for the last connection, and realized your junction box doesn't have room for it. The Shimano EW-JC130 Y-Split Connector solves this by consolidating two E-Tube wires into one port. Both shifters can share a single junction input, which frees up the other port for a charging connection, wireless unit, or satellite switch.

The most common application pairs this Y-split with the EW-RS910 bar-end junction, which only has 2 ports. Without the splitter, one port goes to your left shifter and one to your right, leaving nothing available for the wire running down to the rest of the system. The Y-split lets both shifters merge into one port, keeping that second port open for the main E-Tube wire heading to your frame junction or battery. It also works anywhere else in the system where you need to combine two inputs into one connection point.

Shimano offers several length configurations to match different handlebar widths and junction placements. The SM version uses 350mm for the left shifter leg and 450mm for the junction leg, while the MM version extends both primary legs to 550mm for wider bars or cockpits where the junction sits farther from the hoods. The short 50mm center section connects the right shifter and sits near the stem where the three wires converge. These cables can't be trimmed or shortened, so measure your routing path before ordering to make sure you're getting the right size for your setup.