The Shimano SM-EW90-A is an electronic shifter junction box designed for use with Shimano Di2 electronic shifting systems. It is intended for cyclists who want to integrate additional controls or require a centralized wiring node at the cockpit. The unit mounts neatly under the stem and provides three E-Tube ports—typically two for the handlebar shifters and one for the downtube junction connection. The SM-EW90-A features a battery level indicator, a charging port, and can display the current gear position and adjustment mode. Its straightforward installation and tool-free design make it a practical choice for both new builds and upgrades, especially in standard road bar setups where handlebar-end junctions are not an option.

This junction box works with most Di2 systems before the 12-speed generation of Dura-Ace R9250 or Ultegra R8150 but is not compatible with older 10-speed Di2 generations like Dura-Ace 7970. It uses EW-SD50 cables and is not intended for setups requiring multiple satellite shifters; for those, the 5-port SM-EW90-B is recommended. The SM-EW90-A is suitable for riders who value clean cockpit wiring and easy access to battery status, and is especially useful for those who require a secure, central connection point for their electronic shifting system.