Wiring route and connection for adding speakers to rear doors in 2015 access cab?

Heyas TacomaWorld! For my birthday, my present to myself is going to be adding speakers to the access cab rear doors. I have found a hundred tutorials and HOWTOs for changing speakers in crew cab doors or upgrading the front door speakers, but none for running the wiring and the connection to the stock head unit.
Does anyone have or know of a step by step tutorial on that process; particularly the head unit connection. The couple of videos I've found sort of skip that relatively important bit.
Suggestions?

 

R2 is on the Head Unit.
IE1 and IL2 are behind the kick panels.
BF1 & BG1 are behind the rear side panels (not the doors)

 

Thank you!
Ah, you are in PR, nice. My wife is from Luquillo.

 

Opposite south corner here