Automatic bight light switch?

When I was pulling the engine I noticed this behind the galloping horse
Due to the over spray I thought it was structural I never paid attention to it. On closer look it seems there is an optic of some kind painted over, then I saw the wires leading to the passenger side light harness.( Thank the mustang gawds the oem wiring harness hasn't been butchered.)
So, is this an auto dimmer for the bright lights? If so I'm wondering if it will still work.

Thank you, both. I'm replacing the OEM AC with an aftermarket system.
The wiring from the sensor runs into the parking light, turn signal harness. I'll try to trace it back and see if it operates.
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