I used the rain input on a Davis Temp/Humidity station. The pinouts for the Davis rain collector are:
Input/Output Connections
Black . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Unused
Red . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Switch terminal
Green & Yellow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Switch terminal
But this is somewhat ambiguous. I wired the NO terminals of the RG-11 to match these "RJ-11" connector terminals on a Davis SIM rain channel. Maybe using an actual Davis cable and cutting off one end might be the best bet. I had to use a slightly larger wire than the RJ-11 connector 24 gauge wire since the screw terminals on the RG-11 would not tighten on such a small wire. I soldered short wire stub to the 24 gauge and put heat shrink tubing on it.
I had some trouble at first with the RG-11 not registering counts. I found that I would get a count when I plugged in the connector. I eliminated one of the wires until I got the closure to the rain input to work correctly. Sorry, I didn't document what I did very well. The RG-11 rubber o-ring is difficult to get to seat properly, otherwise I would go and look at it for you. It was somewhat of an ordeal to get it back together properly.
The output that was in my posting is from a Davis Envoy8x, which allows multiple "ISS" units. I have the "real" ISS configured on Station #5 and the Temp/Hum station on #3. The accuracy seems to be variable compared to my CoCoRaHS and Davis gauges. Sometimes they are reasonably close other times, way off. The "RainX" treatment seemed to make an improvement.
Greg H.