I wonder...
Is it possible the previous owner had a problem with the propane sensor, and by-passed it with a switch? The reason I wonder this is because of all the RVs I have ever owned, I never had one that had a switch to control the propane solenoid valve (emergency shut off valve). That valve has been connected to a propane alarm in EVERY case where one was installed!
Of course, it is also possible that there was never an alarm installed, but the valve was installed with a new regulator, and the switch was put in to control it.
Either way, it appears it can NOT do what is is designed to do, which is shut off the propane in the event of a gas leak inside the coach, and alert the occupants to the leak.
Personally, I would either remove the solenoid valve (is is pretty much useless) or install a propane alarm and connect the valve properly.
But, that's just the way I think.
Good luck.