Dimmer Signal Circuit (TO 12/2010): Description
WARNING: This page is about a different car, the 2011 Toyota Avalon. However, it is still accessible from the selected car via links, so may be relevant.
The radio receiver assembly uses this circuit to communicate with the body ECU via a direct line. The body ECU uses this circuit to send an auto dimmer signal to the radio receiver assembly. The body ECU detects the position of the light control switch according to the resistance. When the light control switch is set to the head or tail position, the resistance between the head or tail terminal and body ground is below 1 Ω. When the light control switch is set to the head or tail position, the body ECU sends an auto dimmer signal to the radio receiver assembly. When the radio receiver assembly receives an auto dimmer signal from the body ECU, the radio receiver assembly causes the instrument panel illumination to be dimmed.