Anyone building or refurbishing a Di2 setup on a road bike from the 11-speed era knows the junction box is the piece that ties the whole system together, and if yours has failed or gone missing during a frameset swap, the SM-EW90-A is the direct replacement Shimano intended for that job. It's the below-the-stem Junction A that connects both shifters to the down-tube wire running back to Junction B, and it doubles as the charging port when you're running an internal seatpost battery. Three E-Tube ports handle a standard road setup: one for each shifter, one for the down-tube run.

The small LED on the face of the unit gives you battery level at a glance and switches the system into rear derailleur adjustment mode when you hold the button. That's the mode you use to fine-tune indexing at the roadside without pulling out a phone or connecting to E-Tube Project. Press and hold longer to trigger crash-protection reset on the rear derailleur, then spin the cranks while it cycles through the gears. It's the same interface Di2 riders have used for years, and it's genuinely useful when something drifts out of index mid-ride.

Compatibility is the piece most riders need to double-check before ordering. The SM-EW90-A is designed for 11-speed Di2 generations built around EW-SD50 wiring—Dura-Ace 9070 and 9150, Ultegra 6870 and R8050, and the corresponding 105 R7050 groupsets. It's not compatible with the newer 12-speed Dura-Ace R9250 or Ultegra R8150 systems that moved to EW-SD300 wiring, and it won't work with the original 10-speed 7970 Dura-Ace Di2 that predated E-Tube. If you're running a bike with the internal EW-RS910 bar-end junction, the SM-EW90-A can replace it as a stem-mounted alternative provided you're on 11-speed.... Read More