An idle reduction system for use with an engine can include a main unit including a controller, and a relay controlled by the controller. The relay can be electrically connected between an ignition switch and an electrical power source for starting the engine. A method of reducing idling of an engine can include connecting an idle reduction system, thereby permitting the system to shut down the engine in response to one or more predetermined conditions, the idle reduction system starting the engine in response to at least one of: a) battery voltage being less than a predetermined level, and b) engine temperature being less than a predetermined level, and the idle reduction system controlling operation of at least one of: an auxiliary air conditioner and an auxiliary heater.