I just installed the F90BT in my car and I've used the navigation system just enough to notice that the distance to an upcoming turn or destination always seems to be off by 50-to-400 feet. For instance - when approaching a "T" in the road where I must make a turn, I watch the number for feet to the intersection count down, and it never hits less than 50 feet. I'm not sure if this unit is designed to signal when you get to the point where you are supposed to turn, but mine never has - possibly because it thinks I have not yet reached the point to turn. (My portable Magellan Maestro chimes at the intersection.) My GPS antenna is on the front dash, using the sticky metal plate, and it seems to be getting a good signal. I do not have the speed sensor wire attached. Could the speed sensor wire make that much of a difference? Has anyone here tried using their unit without the speed sensor wire attached and then attached it later? Did it make a noticable difference in GPS accuracy? (I'm not sure I can find the speed sensor wire on my own in my 2007 Kia Rondo, but I necessary, I may take to to the dealer and ask them to attach the wire.)

I run the F900BT without the Speed Sensor wire connected in my Nissan Murano and it works fine. It is only meant to help with accurancy when you go into a tunnel so the unit can predict roughly where along the road you are until you get reception again.

My car does not have a speed wire going to the ECU, rather it has a CAN signal so I cannot tap into it.

I have the VSS hooked up on my 1990 Toyota 4X4 and i does not make a damn bit of difference as far as accuracy is concerned with or without it ..it is the same

Like was said before. It is probably needed when in areas of poor reception to aid in navigation as far as I know.

Bud