Hi, if you haven't found it yet, on my 2007 Optima it is right in the center of the dash, nestled close to the windshield glass. As my base model did not come with Auto Lights, I carefully removed the dark round plastic dome-shaped dummy plug with a new working sensor, being careful not to lose the actual wiring connector down inside the dash by securing it with a bent hooked wire as I removed the plug. I also easily upgraded the left-side light switch lever stalk, just exchanging it with the new factory replacement, which comes with a Fog Light and Auto Light control. Access is made simply by unscrewing and carefully uncoupling the halves of the shroud shells mated around the steering wheel column to expose the left side stalk, which is easy to separate, expose and replace.
The in-dash wiring already in place simply hooks up and works perfectly with the new plug and the light switch, but for cars such as mine, without factory fogs, I had to run the additional wiring when I added my newly installed factory fog lights.