Need more details... What was the difficulty, are they trying to install the external wiring harness instead of the internal, etc?

That should be pretty straightforward. I did my own Di2 wiring and I am not even a bike mechanic. The wires are all long enough to have sufficient slack to connect all of them first before pushing them back into the bottom bracket and covering up with the plastic cover.



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Carl wrote:

might have been trying to send the wrong end through ... Skinny ends of the connections enter frame from the outermost points and meet at the BB. Anti-rattle zipties can make the entry at the rd exit a bit tight, but they will fit through.

ETA: fixed smartphone typos

that's the internal wiring harness...bet he was trying to run the external?

if he doesn't already have it he'll also need the SC Di2 conversion kit PN 422802 which includes, in addition to the Di2-specific rear brake cover, our own short battery rail. the spacing on Shimano's short rail isn't quite right for the mounts on that brake cover. 1.5mm hex is all you need to remove the stock rail bolts and make the switch.

one length to the internal harness and it covers all five sizes of SC. if you can find one, you're good to go. I'd love to help with availability, but I can't see into our non-domestic warehouses.

I don't know if I'd call it daft, but certainly more difficult...cable length now does come into play as there are several options for various frame sizes. Also need to figure out how & where to attach the main junction at the BB.