OK - this just keeps getting stranger.

On the first diagram at the top is the connector for the rear wiring harness. From what I can tell it's like this:

Black (2) is 12V for tailights
Dk Green (3) is 12V for left brakelight
Brown (6) is 12V for right brakelight

At the connector, I get 12V coming in on 3 & 6 when I press the brake. (Or on each of those individually when I hit the blinkers). So I think that eliminates anything to do with the turn signal switch.

I applied 12V to 2,3 and 6 on the connector going back to the brakelights, and got nothing. I connected my ohm meter and noticed that all three of the connections have continuity to ground, and to each other. I'm assuming that's OK since the bulb itself in the tailight goes to ground.

So - if I apply 12V directly myself they do not work, if I step on the brake it's applying 12v in that same spot and it doesn't work. But the Blinkers (which apply 12V at that exact same spot) do work. How can that be?