Cadillac 1994 Eldorado Owners Literature page 128

Light Sensor
Fog Lights (ETC)
Use your fog lights for better vision in foggy or misty conditions. When
you press the upper fog light switch, a small indicator light will glow to
tell you the fog lights are on. To turn them off, press the switch again.
When the twilight sentinel is on, the headlights will turn off
automatically. Your fog and parking lights will remain on.
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