tested everything I can and problem seems to be to rear derailleur feed out of Junction B connector -extension cable/derailleur is good and rest of bike and shifting work good so this is all I can figure out after many many hours. Anybody got one to spare?? I have attempted to attach pic? Anyway it is little connector box out of old 7900 series Di2 has 4 wires with plugs/connectors coming out of it that hooks rear derailleur, front derailleur, battery and front end shifters. Happy to pay for part , for shipping but have hunted web and no one seems to have part so someone's spare parts pile may be only solution. dviney7@gmail.com