The picture is actually the CB install but it does show the headset junction box too
Remove the left pocket, on the inner wall at the bottom there is a removable grommet where the antenna cable comes in.
On the picture the coupler holder is actually the fairing where the cables route.
B is the passenger, you will need an extension for that too reach the passenger, Sierra.com may have that.
C is the antenna
A is the driver cable. There is a special grommet that comes with the kit that replaces the solid grommet, I don't bother using the grommet, I just route mine over the front of the plastic cover.
You can get Holders for the cables from Sierra.com also so they don't flop around item 85