I did that on my 2011. There is a wire you tap on the headlight switch assembly. They do dim, though I think I need to add a resistor to it to step it down a bit more.
Here is my thread with the info. I posted wire diagrams and pictures.
http://www.ramforumz.com/showthread.php?t=171419
or search for under dash LED
Here is my thread with the info. I posted wire diagrams and pictures.
http://www.ramforumz.com/showthread.php?t=171419
or search for under dash LED