Fuel level sensor on petcock

Hello I have a 1977 bmw r75 and I am building a cafe racer I had the idea to make a fuel level sensor to it. I see that some of the older moto guzzi bike had them. The r 75 has 2 holes for 2 pet cocks would it be possible to use one of the holes for a fule sensor. And do those sensors power a on/off light or a gauge. I have not seen any one do this. I thought that it would be a unique part of the bike. Thanks