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I am planning out a Di2 setup with the Ultegra 6870 series, but I don't need to run a front derailleur. I am making a 1x11 setup. Is it possible to connect the shift level (I am using the ST-R785 levers) directly to Junction B, so I don't need a Junction A at all?

I know for internal batteries, a Junction A is required for charging, but with an external battery, it shouldn't be necessary. Does Junction A do anything else essential? It'd be awesome if someone with a Di2 setup (especially an Ultegra 6870) could test this too.

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  • That's way newer than any kit I have ever worked on. I don't know if you'll get an answer here. If you find an answer elsewhere, please do post it here for completeness.
    – Criggie ♦
    Commented Mar 8, 2016 at 2:47
  • Thanks Criggie. I believe my question could be answered by any current Di2 system that runs the 2-wire interface, so the 6770 should work similarly. I think the old 7970 (Dura Ace) is different, as is the newer 9070, so those probably wouldn't be similar.
    – Hari
    Commented Mar 9, 2016 at 2:48

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According to Slowtwitch Shimano needs one junction A in the system otherwise it won't work.

You can skip junction B.

It may cause some interesting wiring.

The 6700 series (EW6770) junction may make things smaller/easier.

This is the same answer for all current e-tube di2 systems. (6700,6800,9000)

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