Need to figure out what's going on with 38 gallon propane tank

[TXheat]

So there is supposed to be a full tank, it's a electronic valve and there's supposed to be a manual valve but can't be found As you can see in the photos it looks like the wiring for the valve cut off switch is disconnected and there is no gauge on the tank the closest thing is the readout and the control panel which we can't make sense out of. The propane when the gas range is used lights but goes out and the refrigerator when switched LP says FL no which means there's no propane. There are no places that do inspections of fixed tanks that we know of so this is something we either have to hire a RV repair who has experience with this or DIY for starters it seems like getting a analog gauge would be a good idea to determine just how much is in the tank if anything. Either the tank is full and there is an issue with the electronic valve or the tank is empty. One question needs to be asked is it safe to install the gauge on a tank that we know very little about.?