I wasn't sure if the internal mounted junction box was making life more difficult anyway, as don't I need access to the box to charge the battery (I've got the seatpost mounted one)?
You can use the EW-RS910 bar-end junction instead of the usual SM-EW90-A 3-port junction.
You can use the EW-RS910 bar-end junction instead of the usual SM-EW90-A 3-port junction.