The Fuel Sending Unit is responsible for sending an electrical signal to the fuel gauge to indicate the level of fuel in your tank. The fuel sending unit uses a variable resistance to generate the variable electric current to indicate the fuel level. The mechanism consists of a foam float that is connected to a thin, metal rod. The end of the metal rod is connected to the variable resistor. A wiper, that slides on the metal strip, is connected to the gauge and conducts electricity from the gauge to the resistor. When the tank is full, the wiper is closest to the ground and the resistance is at the minimum while the current is at its maximum, therefore making the gauge indicate the tank is "full".