Generator Signal Circuit: Description
WARNING: This page is about a different car, the 2011 Toyota Corolla. However, it is still accessible from the selected car via links, so may be relevant.
When the engine is started, the generator rotates and a pulsed voltage signal is generated. This signal is used by the A/C amplifier. The generated voltage signals sent from the generator are used for controlling the number of the heater elements to be heated.