Good Method to Add Wiring For Add-Ons

This pic is a section of what I printed out from mymopar.com.
What I need to know, and what it doesn’t show, is where the brake failure light circuit gets its 12v. The fuse it goes to is good, and everything else on that fuse works.
I am powering an accessory fuse block that I added through it. (Powering the relay) It stopped working when I welded on the car and forgot to disconnect the battery. :(