There are three identical 2-pin connectors on OpenSprinkler that connect to 24 VAC, Common, and the Rain Sensor. I like the idea of removable connectors; it makes for quick installation and removal. But, unless they are color coded to minimize (not preclude) the chance of misconnection, it’s an invitation to a damaged board, or transformer. There’s an old saying to the effect that if it can happen, it will.
All it takes is a couple, or three permanent marking pens applied to both pieces of each connector. I chose Red for the 24 VAC connector/plug, Black for the Common connector/plug, and nothing for the Rain Sensor. Maybe Blue for the third one would be appropriate. Any marking system is better than none.