Glue a micro switch to the bottom of the tank. Tie a string to the end of the switch and connect the other end of the string to a fishing bobber. The bobber holds the switch closed until fuel level is lower than the string length. The switch opens.
Glue a micro switch to the bottom of the tank. Tie a string to the end of the switch and connect the other end of the string to a fishing bobber. The bobber holds the switch closed until fuel level is lower than the string length. The switch opens.