Splicing Di2 wires isn't difficult if you know how to solder. You can also get the etube wire coupler (EW JC200).

Another option is to use Etap blips. You would need 2 blips and 1 di2 wire. Cut the plugs off the blips. Cut and slice one half of the di2 wire. Test the wire connects to make sure you know which wires go together. Then solder and heatshrink everything up.

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Strava

Yes, the sprint shifters will work for your setup as they are designed to work plugged directly into existing Road shifters (6870, 9070, etc). There are enough extra ports inside the connection for road shifters for this purpose actually and the sprint shifters won't work without actual shifters installed I believe because they are just a dumb switch with no board/control logic built into them.

Look up sprint shifters pics with road bar setups and you see how they were designed. In order to get enough length use a couple of JC200 junction B which are basically a Di2 wire extender. Buy 2 new wires in the length you need to reach your road bar shifters. This is if you are using something like the R610 shifters which come in pairs. If you want to save costs you could use an R600 single dual button sprint shifters and only require 1 jc200 and 1 new wire. But that is bulky and harder to integrate cleanly into aero bar extensions imo.

No need to buy a 5 port junction A even if you are adding true TT bar end shifters. Even then you could just use a 4 port internal junction B instead and hide it inside the aero bars and get an extra wire to join them together. Assuming you bought new open ended extensions.

I believe all the new e-tube stuff can work independently, so the sprint shifters can go on their own into a junction box. That's what I'm going to be running after this weekend, SW-R9150's epoxied onto Bontrager XXX brake levers. I've plugged them directly into a 5 port junction without issue and they actuate the derailleur correctly. I think the previous generation Di2 (10 speed stuff) the sprint shifters were just dumb switches.

Airstryke has a little hole at the front


Route the di2 cable through that and out the back of the extension.
then I'd link the two STI levers with an SD50 and plug the sprint shifter into the 3port EW90. That way you can easily remove the aerobars if you don't need them.
As mentioned - JC200 is the best way to extend cable reach. Or if you use two sprint shifters - a JC130 Y-junction + a pair of JC200s.

I like your overall suggestion, but regarding the quoted text: Do R610 sprint shifters still have the unique plug such that they can only go to the STI levers? or can they go direct to the junction? Lots of online documentation/discussion on this point, but most of it from 2013/2014... Essentially says these are dumb switches that need the circuitry inside the lever. Thanks, -AGW

Edit: Maybe you were referencing the SW-R9150 "climbing switches" for the switches, with their standard plug? Seemingly just in small in size, but perhaps a little more awkward to try to mount on the bar? I struggle to imagine a clean mount for the 2-button R600, especially given how the wire is positioned relative to the orientation of the unit.

http://carltonbale.com/...ng-you-need-to-know/

The R610 Sprint Shifters won't work - they have a keyed portion on their plug and ONLY connect directly to the 3rd ports on road, non-hydro shifters (9070, R9150, R8050)

As you mention in your own edit, the SW-R9150s would work (and what I'm planning on doing for my road-bike-turned-tri for Whistler 70.3 this year). You could run those from the end of your aerobars, link them with a single JC41 4-port Junction B, then connect with a single wire (of appropriate length) to an open port on your left or right Shifter, if one is available

~ Doug

Thought I'd return back with the end result in case its of benefit to someone in the community:

https://imgur.com/a/FgIJwde

Did a pair of the SW-R9150s. Bought a 700mm SD50, cut it in half, and had a buddy splice/solder the two pieces to extend each of the buttons. Drilled a hole in each of the bar plugs to get the wires out, then plugged them into a (new) 5-port junction. The soft rubbery mounts included with the SW-R9150s made mounting easier than I imagined.

Note there is no way that a JC200 in-line junction was going to fit into the wiring hole atop the Airstryke (thus the splice).

I paid a bit more than necessary with the 5-port upgrade, but it saved me having to buy another SD50, a more complicated splice, and a trip to the bike shop during race week (I leave bar tape to the professionals).

I think the install looks reasonably clean. The splice is nicely shrunk-wrap up, but I'll still use a piece of putty or something to plug up the hole atop the bars where the wires now enter as an additional layer of weather-proofing

Looks great nice work

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the world's still turning? >>>>>>> the world's still turning