shimano - The best way to connect aerobars with Di2-shifters to bike w/ Ultegra 8000 Di2 and the junction box in the bar end? - Bicycles Stack Exchange
Shimano EW-RS910 Di2 Junction (A) Control Box (Only Fits For Bar) Black | eBay
How to wire up new Bar-End Junction A for Di2 (EW-RS910) - Page 3 - Weight Weenies