How does a fuel heater work in a diesel engine?

The fuel heater in a engine gets activated by the glow plug cycle. The heater always has 12 volts of electricity on it. The heater in the engine is usually mounted on three or four pads. These pads have a temperature sensitive resistor. One thermistors is connected to the ground through the mounting of a metal heating plate, the heater part of the thermistor is connected to the other side. The 12 volt is always the heater side when the ignition key is turned on, and it heats the heater. The mounting pads start at a low ohm with low voltage, and go to a high ohm.