My experience may help some. I have a 2004 Forester XT. I hired Circuit city to install my D3, they were having a special for free install so why not? Anyway, they would/could not install the VSS wire. Everything else was installed ok.
I got info regarding the location of the VSS wire, as pin 10 of a 20 pin plug in the ECU. I took everything apart, did the bypass and found the ECU underneath the metal cover plate in the passenger footwell underneath the glove compartment. There I found three plugs, each with many wires, several of them the green/yellow color the VSS wire is supposed to