Shimano Di2 internal frame junction box.

• Frame Junction Box connects via SD50 E-tube wires to four different points: front derailleur, rear derailleur, cockpit junction box and battery mount
• All Di2 components on the bicycle require the same firmware version. Using Di2 components with different firmware versions may cause malfunctions
• Use Di2 system checker to update component firmware from http://e-tubeproject.shimano.com/