Webasto control unit M075 receives a power supply directly from the battery supplied by programming device H110, supplied in turn by a line protected by fuse F58 located in optional junction unit B101.The heater pump is ignition-operated and fully managed by control unit M075 or device H110. The ignition-operated supply is governed by relay T24, also housed in optional junction unit B101. The relay is "normally closed" type; i.e. relay pins 30 and 87 are short-circuited at rest. When inertia switch I050 cuts in, the earth reference at pin 86 is no longer present. Under these conditions, the coil is no longer excited and the internal relay contact opens. Under these conditions, the pump of heater N044 is no longer supplied from the battery. This strategy is used as a precaution to prevent or at least reduce the risk of fire in the case of accidents.Sensor K042 supplies control unit M075 with external air temperature readings that are used to ensure correct heater system operation.Control unit M075 supplies the supplementary heater motors, where present in the vehicle, from pin F to provide a direct power supply from the battery via shunt J035.