Heated Seat Circuit
Car seats are heated by placing heating elements in the seat cushions and backrest. They are coils that are similar to those found in an electric blanket. They resist the flow of electricity, converting it to the heat energy felt in the cushions. Notice that the heating elements in the image run in series. This means that an open or excessive resistance in the wire or plug leading to one element will affect the other.
The seat cushion has a temperature sensor. It is an NTC or negative temperature coefficient sensor, a type of thermistor used to sense temperatures in different automotive systems like air conditioning and engine cooling. The module uses the signal from this sensor for safety and to regulate temperatures for HI and LOW settings.