Avic 940BT speed sensor

[RoadkingC6]

I have the Avic 940BT in my car, I have a 2005 Corvette with a digital speedometer and a HUD in the car, the problem is my speedometer is not registering the speed on the dash or at the HUD unit, the tach and other functions are good, i had the Pioneer installed at P.C. Richards over a year ago and everything was fine until recently, i have searched the Pioneer disc on the computer to find the wiring diagram for installing the unit to the car, however the disc only shows how to use the radio functions, my questions are where can i get a wiring diagram showing the radio, speaker and all connections to the car, i don't need the wiring directions on the internals of the radio that would be beyond my abilities,  I am suspicious of what i believe is called the VSS wire which i believe ties in with the speed sensor for the GPS part of the unit ,  I am thinking maybe the installer spliced this wire into the car and maybe the splice came loose and is causing my speedometer not to work I would like to know what the identifying colors are on this wire to track it down and check out the connection,  i'm not sure if this is the problem or if that wire would affect speedometer functions,  but getting to the radio in the car is not that difficult to check it out,  my next place to go is to remove the speedometer cluster which also isn't that difficult but i would rather go to the radio section first, any thoughts or help would be appreciated .