which mirrors do you have? BT or regular... if you have the puddle lights i think that'd be the wire you wanted... also if you have the bed lights that may be what you're looking for as well.. i'd dig up the wiring diagrams but i'm at work.. perhaps tonight if no one else chimes in.
From what I've been able to dig up there is a red/white wire at the BCM on pin 62. Which brings up the questions of, which connector is this on the BCM (there are multiple ones)? And also if I tap in at the BCM do I need to put in a relay?