When the automatic light control sensor detects level of the ambient light while the light control switch is in the AUTO position (or in the OFF position for the models without the AUTO position), it transmits a signal to the light control unit, which turns on the taillights and then the headlights depending on the ambient brightness.
The system also has a function that turns on the taillights but prevents the headlights from turning on briefly in cases where it becomes dark for a moment, such as when driving under a bridge or down a tree-lined street when ambient are bright. However, if after a certain lag time has elapsed, the ambient brightness is lower than a specified value, the headlights will come on.
There are various types depending on the model, such as a type in which the automatic light control sensor and light control unit are one unit or a type in which the taillights and headlights come on at the same time.
When the automatic light control sensor detects level to the ambient light, it outputs a pulse signal to terminal A of the light control unit. When the light control unit judges the decrease in ambient brightness, and activates the taillight and headlight relays to turn on the taillight and headlight.
When the light control unit judges an increase in ambient brightness, the taillights and headlights go off.