Ignition, heat and start key switch
Ignition, heat and start switches no longer play a major role in modern vehicles, but are still in demand as spare parts for older vehicles. In these switches, a further circuit PREHEAT is inserted between the ON and START positions. In diesel vehicles, this is used to preheat the combustion chamber before the starter engine is activated.
In modern vehicles, the preheating is controlled electronically, so that often only ignition and start switches are installed here.