Do I need to contact the vss wire for that function to work? I hooked it into the wire it says to but nothing. My screen says the function not available now. Anything? FYI...I have a 95 chevy fullsize

I believe you have to go on into the settings menu and then hardware info to read if vss is working. If it just says 0 while driving then you don't have it connected to the right wire. The gauges don't work right away after connecting vss. Sometimes they take a day or two until the unit calibrates to the vehicle.

Sry to double post but you have a 95 chevy full size what? Specifically what type of truck, and what wire did you connect it to.

I have a 95 chevy fullsize 1500 w/ the 5.7. I attempted to hook it up to a green/white wire which is on a module under the ecm below the glove box. I didn't get anything from it.

I was able to get the unit simple hybrid mode so it is showing the speed now but it is better to hook the wire up? Also if I leave the wire unhooked up, will the speed not work if I have no GPS signal?