Shimano GRX RX 815 Series Dealer's Manual page 88

INSTALLATION/REMOVAL
Installing junction [B]
2.
Connect the electric wires to the E-TUBE port on junction [B].
Be sure to push it in firmly until you feel a click.
3.
Adjust the excess length of the electric wire.
Wind any excess length of the electric wire to the groove on the top of junction [B] as
indicated in the figure below, and adjust the length.
Electric wire
Rear (rear side)
Example of adjusting the length of the electric wire to the front side
Example of adjusting the length of the electric wire to the rear side
Top (frame side)
E-TUBE port ×4
Front (front side)
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