My Dodge had a stubbed wire for a third brake light in a cap/camper shell sticking out of the main wiring harness. I think I have read that GM also has this, but I cannot find where I read that. I'm mounting lights on my toolbox, one of which is a tail/brake light bar (no turn signals). I'm looking to tie into that circuit on a 2012 2500HD...anyone give me an idea where I should look (or if this wire even exists?)?