Wiring harness for side mirror turn signals

[doodman4321]

Can anybody tell me how involved it is to install the wiring harness for turn signals in the side mirrors? I popped the mirror off of my ‘12 SCrew just to check before ordering the lights, and the only wire run through was for the mirror adjustment motor. The mirror side just has a black piece of plastic where the signal would go and then a reflector on the other side. I’m decent enough at following instructions, I just haven’t done much electrical work on vehicles before.

 

[doodman4321]

Just got off the phone with the local Ford dealership, and the parts guy seemed to think that I wouldn't even be able to find a wiring harness specifically for this, and if I somehow did, it would require a major overhaul to get it in and make sure it's tapped to the signals. Sound right? or bogus? Not a big deal at the end of the day if I can't get signals in the side mirrors. I'd just like to provide a little more warning to other vehicles since this thing is so big.