Originally Posted by
TakingMyTime
See, I learned something... it's not a "wart" but a junction box. I thought it had some other function i.e. BT antenna or something like that. Live and learn.
There are at least 3 variations of the A Junction box. Original model mounted under the stem. Next was as a plug in the handlebar end. That required the bar to have holes for the Di2 cables to exit the bar and route into the downtube enroute to the B Junction. A later version mounted into a downtube spot. All the A junctions had either 3 or 5 ports (not sure bar end had 5) for the 2 shifters, plus extra shifter buttons for sprinting or climbing positions. Time trial bikes as example might have 4 shifter buttons, on the end of the aero bar and near the brake levers. With the new wireless Di2, they've done away with the A junction as the shifters talk directly with no wires. Theres also an A Junction box designed for mt. biking which is a combo gear position indicator, BT wireless transceiver as well as 3 port junction, it mounts onto the handlebar next to the stem,