One zone does not turn on

I have a six zone system in my house. Zone 1-6 all work except for Zone 3. I am not even sure if it is connected to anything but when I turn it on with the App, blue light blinks on the Rachio controller but no water comes on anywhere. What is the best way to figure out whether it is connected to a solenoid valve ?

There are some old school (metal) pop heads that I see on my yard that does not turn on at all, so I wonder if my Zone 3 used to control this old system…any help would be greatly appreciated.

Can you send some before and after wiring pictures to I’m sure they can help out.

Thanks and have a great day.