Building out a TT or triathlon Di2 cockpit almost always exposes the limitations of the standard three-port junction box — between aero extension shifters, base bar brake levers, and any climb or sprint switches you want at the hoods, the shifter count runs past what the SM-EW90-A can handle. Shimano's SM-EW90-B 5-Port Junction Box is the answer for those multi-input builds, giving you five E-Tube ports to run up to two pairs of Di2 shifters back to the frame junction over SD50 wires.

Known as Junction A in Shimano's wiring architecture, this box lives near the cockpit and acts as the central connection point between your shift inputs and the rest of the drivetrain. Four ports handle shifter inputs — primary STI levers, aerobar extension shifters, and secondary sprint or climbing switches — while the fifth port runs down through the frame to the rear junction and on to the derailleurs and battery. Any ports you don't use stay capped until you're ready to expand the setup later.

The housing includes an LED battery indicator that reads out charge status when you press the button on the face of the unit: green for more than 50 percent, red for below 50, and flashing red when it's time to charge. That same button enters rear derailleur adjustment mode for indexing, which is where you'll spend time during initial setup or after any derailleur hanger work. It's also the charging port for the internal battery, so you can top off the system without pulling the battery out of the frame.... Read More