Weird Bulb Behavior

You may have a shorted bulb, and I believe it could be any one of the 4 corners. Otherwise it just about has to be a ground and or a short across something else in the harness. I would separate the tail harness at the left kick panel connector, make a jumper with a male flag terminal, so you can jumper power to the pins in the connector, and test operation of the tlamps at will

But on the "removed socket" thing, the tail lamp is getting a ground through the filaments of the turn signal, and vice versa. If you study up, they "reverse" so to speak. With the tail lights off, the turn seems to work, but with the tail lights on, the turn filament on the rear will light when the front one is out, because the two are in series, and with both filaments getting power--and no ground, they cannot light