Shimano ultegra di2 shifter connector question


New Member
Jan 18, 2017
First time poster!

I have a 2017 Giant Defy Advanced Pro 0 with the Shimano Ultegra Di2 groupset. I purchased a climbing shifter, SW-R600. It's supposed to plug into the right shifter, which is (according to the schematics online) should have 3 ports. However, when I pull back the hood, I only see one port which is already occupied by the connection to the Di2 junction box.

What gives? Is it that the groupset that comes with the bike is different from a generic version of the set, or is it that I am just a noob that's looking in the wrong place. I was fully prepared to install the shifter and re-wrap by bars... and now I am stuck.

Help! Any advice would be appreciated.


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Oh, the bike has hydraulic disc breaks, so the shifters are ST-R785. I wonder if that's the reason there is no extra port. And if so, is my only solution to replace the junction box with one that has 5 ports (the current one has 3 and all are occupied) and plug the climbing shifter into that?
Well, more research, should've done this sooner. I think I may have answered my own question. It is in fact the hydraulic breaks. The shifters for those only have 1 port. Some other Di2 shifters have 3 ports, some have 2, these have 1. So I ordered a 5-port junction box to replace my 3-port. Will report back once I receive it and try installing it.

Argh. This should be simpler. On the positive side, the installation of the Di2 D-Fly remote data transmitter could not have been quicker or easier. Five minutes for a noob like me is not bad. Cheers!
Old Bob Cat should be replying to this thread. Until he gets here...

Looking at the D12 Ultegra Dealer manual that's available for download on shimaNO's website (They have a great product support section. The manuals are typical Asian in their cryptic wording and sometimes worthless drawings/pictures) it appears the 5-plug junction box is one option.

ST-R785 Exploded view isn't much help:

Page 42 of the ST-R785 Dealer Manual seems to suggest the 5-port junction box is the method to add sprint or TT bar shifters.
Yep, thanks. I was having trouble finding the right manual. Giant lists the shifter as RS785; the extra "S" was throwing me off. Note to self: RTFM! :)