When performing the bypass, I am unclear on one of the steps. After I place a wire in the unused PIN slot, how do I ground the wire if I have to plug the harness back into the back of the unit? Do you just cram it in there and leave that wire hanging outside of the plug once connected?

Ground the "bypass" wire and the parking brake. That means ground it to the chassis of the car, or another black wire that is already doing that

So all I've done so far is to just ground the light green parking brake wire. I haven't even touched the harness yet and video is playing beautifully. Do I even need to bother putting a wire in the unused slot on the harness?

Yes

So all I've done so far is to just ground the light green parking brake wire. I haven't even touched the harness yet and video is playing beautifully. Do I even need to bother putting a wire in the unused slot on the harness?

So all I've done so far is to just ground the light green parking brake wire. I haven't even touched the harness yet and video is playing beautifully. Do I even need to bother putting a wire in the unused slot on the harness?

Yes, you do. Try driving without and watch what "doesn't" happen (no more video).

Just do it!