Interior light auto dimmer?

Ive seen a peterbilt where the interior lights dimmed automatically after the driver locked his door and walked away.
I was wondering if that's a kit you can buy somewhere and put in. Or is it a peterbilt oem feature.
I've been trying to get one but the guys at Peterbilt didnt know anything about it.
Can any one help me out here?

 

This didnt look like a newer truck. It looked like a 359.
But ohh well...
Any one know if any aftermarket kits are available?

 

Thanks grape. Ill give it a try.

 

Well I got the dimmer and installed it.
Works great.
Got the one for ford and everything works as it says it does.
Had to install it on the passenger door because I couldn't get to the wires on the driver's door.
Big thumbs up on this project.
Now if I just ccould figurr out how to connect all my bunk lights to the dash switch.