6715 speed sensor

Hi,
I have a 2004 6715 and the speedometer is not working.
I assume it gets its signal from the "ground speed detector".
I am unable to determine where the sensor is located.

I have a manual on CD and I have searched through it to no avail!

Does anyone know where the ground speed detector is physically located?
How many wires should be going to it? 2 or 4?
Thanks