Those of you who have burnt out fuel level sensors might be interested. The sensor is actually a thermistor in series with the idiot light.When the sensor is covered in fuel it's kept cool and the resistance is quite high (about 1,000 Ohms). The current through the lamp is not enough to make it glow. When the level drops the thermistor is no longer cooled by fuel so it warms up and it's resistance drops, the current goes up so it heats even faster until it's drawing all the current the idiot l