This is the Shimano Ultegra Di2 Internal Junction Box. This box is referred to as the junction box "B" on a Di2 build. The SM-JC41 is for use with internal wiring setups and is the main center of e-tube Di2 systems. For external wiring setups see the SM-JC40.
- Frame Junction Box connects via SD50 E-tube wires to four different points: front derailleur, rear deailleur, cockpit junction box and battery mount
- Use Di2 system checker to update component firmware from http://e-tubeproject.shimano.com/
- All Di2 components on the bicycle require the same firmware version. Using Di2 components with different firmware versions may cause malfunctions