99 F-250 Super Duty VSS Navigation

OK i have been searching this forum for hours, I installed a JVC KD-NX5000 and had hell finding the black and grey wire. well i did and now im having the same exact problem that this guy below me is having. but a little different my gps thinks im doing CRAZY amounts of speed i drive 20 it thinks im doing 45 im doing 45 its well close to 100MPH. the navi gets way ahead of its self and im assuming it does this because it thinks its doing 100 down residential streets i need help guys. just want to get it done

"I found what appeared to be the right VSS wire but the unit says i'm doing 40 MPH when i'm really doing 20 they told me to get it at the PCM on the drivers side... That was a joke! So they aslo said at a small silver module (Speed control Module?) On the passangers side of the engine bay pin 3 gray/black. Well I found a pin 3 and there was a gray/black wire in it... But it throws my reading off... Maybe the unit was all finished downloading? The navigation unit is the brand new one from alpine. The tech dept said that the VSS wire is only needed to aid the navigation when traveling in large cities with big buildings and tunnels... Anyone ran into this problem with this truck? How can I fix it?"

As the tech department stated, the only time that wire is needed is if you want to see where you are if you are driving in a tunnel, a parking garage or downtown with an abundance of tall buildings that will block satellite signals.