Left side brake woes

p. 8-71 has a functional diagram. Use that with the wiring diagram to make schematic you can follow.

maybe this will help you get started.
Power for the turn signals comes from the ACCESSORY terminal on the ignition switch. From there to the Flasher Module, then to the turn signal switch.
Power for the brake lamps comes from the Primary Distribution Point (a welded splice) which supplies the two fuses that are ALWAYS HOT. One wire from the Tail-stop-fuse go to the switch on the brake pedal. Its an 18 gage pink wire that also connects to the 4 way flasher module.