I want to install a timer switch (it has four wires, red (load), black (hot), white (common), green (ground) to replace one switch in a 2-gang switch box having five incoming cables (see first photo). One switch controls the fan (want to replace with timer), the other switch (3 way) turns on the recessed ceiling lights. I made a diagram and attached pictures.
Which of the two common pigtails will I tie the switch common wire to? Also can someone confirm that my black hot wire ties into the black pigtail? And that I create a new pigtail to tie the red source for the switch to the black of cable #5? Any help would be appreciated. Thanks