There are two quick ways to deal with the problem if you never rely on the rain sensor. The first is the bypass switch in the clock, just slide the switch to off or bypass. The second is to open the panel of the clock and use a jumper wire between the sensor wire terminals. If you can post the model clock I can be more detailed on how to do this.

Thanks Mike
It is a Hardie Irrigation model

P/N HHA11271 6/91

Over 20 yr old!! Inside the control box I see the following wiring setup:

1 white
2 blue
3 blue
4 white
5 red
6 open

2 green wires connected to COM/GRD and of course the AC connections. The backup battery inside was dead but when I swapped in a live one, it didn't help anything.

I never use the programs, just run on manual.

There is also a red wire in the box with the end stripped that is not connected to anything, as if it had been disconnected after assembly. I do have 5 zones so the five wires make sense.

I dug around in the mulch until I found the severed rain sensor wire, shorted the wires and now zone 1 started working!! I assume all is fine now and will try the other zones tomorrow morning so as not to leave the grass wet overnight. Mike, if you can still tell me what to do at the box so as to avoid any future troubles with the sensor, I would be appreciative.

Inside the clock where the two wires from the rain sensor are connected just connect the two terminals with a short wire after removing the wires for the sensor.