So, we've had this low level switch function in our sump tank for awhile. And it's always sucked. We started out with the factory's standard float switch wired to a lamp in the panel, but it would nuisance alarm at altitude and at high power/high angle of attack. I bought a VP03E
to alleviate these problems, since it's optically based it should always be accurate (if there's fuel in the tank, it says full). However, this is a solid-state device, and as such never really operated like a proper binary system. Sure it was bright when it was empty, but it was always sort of lighted even when full. Maybe I had it hooked up wrong, I'm not sure, but this year when we filled it up, the light was always bright. I learned a lot more about these devices than I ever cared to, but in the end I just got a new one and hooked it up to a relay to get the functionality that I wanted. Call me a cheater, I don't care.