I am trying to replace ESP-ME Rain Bird by RACHIO-3 but I could not understand color code wiring. There are 3 sky-blue wire attached together with black wire.
@Kebal - those blue wires are the common wires. Just keep the same setup ( i.e. the three blue wires wire nutted together with a black pig tail wire) and connect the black wire to a Rachio C(ommon) terminal.
Welcome to the community.
Wow, your installer didn’t skimp on the wiring! That is some heavy gauge wiring right there!
Thank you.