Is it the one in te pass kick panel? If so, check to make sure you don't have more than one wire of that color and if so, check the other(s) for a correct connection. If needed, I will get a pic of my connection after the rain stops and Noah brings his Ark by...
No, mine is bypassed as well, and that does not effect the speed readings, only allows for route inputs and viewing of DVDs while driving. Once the rain stops here in central Arkansas and the ground dries up enough, I will take a pic for you. It may be tomarrow, though. I have had 15.5" of rain at my house in the past two weeks. I'm ready to see the sun!
Not totally. The D3 (like all other Pioneer nav units) has a built in gyroscope. It measures even the slightest movement and can correct itself as you drive. The weather is really nice today, so I will try to get a pic today.
OK, here's the pics. In the first one you will see the location of the wire you need. I also dug a little and found another white/orange in a green plug, this is not the wire you need. That one you can kinda see in the second pic. If your white/orange is in the same location as mine, you may want to check how good the connection is.
Sounds more like a DC 5+ volt wire from the computer, not VSS. I would have one more look (just to be 110% sure) and maybe let a pro look at it. I know for me finding the VSS on some cars is almost impossible, and sometimes I have just let the install go without connecting it. Mazda 3 and Merc C230 come to mind, but most Mustangs have been fairly simple for me (or maybe just lucky).