Wiring Third Brake Light on Camper Shell

ok I have been searching for the answer to the same question, I just got a leer shell and I wanted to hook up the brake light, but the brake lights on my truck are also turn signals, so I'm looking for the right wire but no luck, not even in the trailer wiring 'cause they are brake/turn also
worst case I'm going to bring a new wire from the truck's 3rd brake light all the way to the back and hook up the shell light to that so that it doesn't blink when I turn the turn signal on!!
my question is how did you guys hook up the camper shell brake light?
I have a '07 silverado LT1 NNBS with the towing package, any suggestions?

I'm unfamiliar with the wiring harness in NNBS, but you could do it with a relay and diodes. If what I just said confuses you, it'll probably be easier to run a wire from the fuse box or cab from the existing 3rd brake light.

look in the trailer wiring harness under the truck for a light blue or green wire tagged "CHMBL" (Center High-Mounted Brake Light )
this is the wire you want

thank you for the info guys
ibanender I found the wire in the junction box mbec x9 pin 3 but I didn't want to run a new wire from there to the shell just yet I still want to hear more opinions, and as for the relay and diodes that is way to complicated for me!!!!
bigblue4x4 I will be looking for that wire and tell you the results
you know when I got the shell the previous owner (with the same kind of truck) had it hooked up to some wire right behind the 7 pin trailer connector but he didn't do it and he didn't see how it was done so what you are saying makes sense and this is the 2nd time I hear this!!! (I mean read this)