Ray, just confirmed that my rain sensor is in fact the Hunter Mini-Clik (see previous post).
Tonight I re-tested the rain sensor wires (disconnected from OpenSprinkler) with my multimeter. As the external sensor itself was dry, I had to use the little “self test” button on top of the sensor to trigger the rain shut-off function (i.e. open circuit). What I found:
No rain (self-test button not depressed): closed circuit — almost 0Ω reading between the wires
Rain (self-test button depressed): reading between 4 to 5 MΩ between the wires
I re-checked several times, tested by connecting to the screws on the plug, as well as on the raw wires (green plug removed), and I was always getting 4-5MΩ reading.
Do you think this could be the problem? I wonder how I can tell if this is “in spec” for this particular sensor (in which case the sensor is just not compatible with OS), vs the sensor is truly defective. Is this outside what OpenSprinkler expects to see?