Originally Posted by
mtseymour
If I'm not mistaken, the captain's BB shell doesn't have enough room for internal Di2 wiring. I don't think that you can cut slots in the BB shells because they may interfere with the welds. Your only option may be to drill a hole in the bottom of the down tube for the Di2 wire to exit, and another hole in the bottom of the boom tube for the wire to re-enter the frame.
It would also help to place the battery in the stoker's seatpost. This will allow you to run a single long wire from Junction A (or MT800 display) through the down tube and boom tube to the Junction B in the stoker's BB. The Junction B will connect the Junction A, internal battery, front and rear derailleur. The Junction B may be stuffed in the seat tube or boom tube where practical.
Thanks for the comments.
The eccentric im using is the ProblemSolvers Pressfit for 24 spindle eccentric bottom bracket. It allows the bottom bracket shell to function without needing to have slotting of the BB shell. I will be using a sheet of plastic cut and inserted to keep the wires pressed into the inside circumference of the shell just in case though.
The battery can be in any seat post. My derailleur wires are just extra long instead of the downtube wire being long. I looked at what was available and the lengths of my bike and a 1600mm wire would have been tight to get from the handlebars to the stokers BB area as well as we have an admittedly cheap suspension post that wouldn't take the battery at all for the stoker.
As it sits, its totally functional and just needs assembly.