Question
I am attempting to wire in the subject rain sensor into a Rain Bird #ESP-6si Control Panel, which has no terminals for a rain sensor.  Can you advise how this sensor can be added?

Thanks!

Answer
Thanks for your question.
The sensor will need to be powered. Connect the 2 red wires from the sensor to the "24vac" terminals of the controller. The easiest way to find them is follow the power wires coming from the transformer. The terminals they go into is the 24 vac.
Next you will have one or more common wires coming from the valves, they will be on the "COM" terminal and are usually white. Disconnect them and connect the "WHITE" wire from the sensor to the "COM" terminal.
Now, connect the wires you just disconnected from the "COM" to the yellow wire from the sensor.
What you have done is interrupted the common wire which is connected to all of the valves. When the sensor activates it doesn't allow a complete path for the electricity to run. It goes out the zone wire but can't get back to the controller, because the common wire has been "severed" by the sensor.
Good luck.

Matt