Unscrew the monitor device mounting screws and look for an unconnected wire behind it.
I am guessing from what you described that you have the standard KIB (brand) tank levels and 12 volt electrical test monitor. Here is a link to the manual on that from our library. THIS MAINLY ELECTRONIC MANUAL IS HARD TO FIND IN THE LIBRARY AS IT IS FILED UNDER "PLUMBING". Probably should be filed both under "plumbing" and "electrical".