The blue wire on the Scosche does nothing. When you get your antenna adapter connect the blue wire from the Pioneer harness to the blue on the antenna adapter.
I tested the blue wire in the Scosche with a multimeter while plugged into the Nissan harness and it doesn't do anything.
I connected the speed signal to the yellow wire shown on my post
here (pin 18). I just got my install done late last night on my 920BT so I haven't checked the ecco function to confirm but I'm sure it's right.
I can tell you though I read another guys question regarding this wire. He was told not to connect it because it would not allow you to play movies ect while the car is moving. This is wrong. As long as you have the bypass done on the AV harness it works. I confirmed this last night. I was able to play a DVD while driving and I have the speed wire connected.