Most of the Granada Scorpios have an electric speedometer, it is run (along with cruise control and 4th overdrive gear in an auto box) from the Vehicle Speed Sensor (VSS), which is located on the underside of the gearbox, behind a heat shield to protect it from the heat of the cats, it is a small device, usually with an orange cog on it, these frequently go and cause your problem.

You could try this thread from another forum I am a member of, Granada and Scorpio Online;

http://www.granada-and-scorpio-onlin...&highlight=VSS

This refers to a 4x4, and the VSS is on the front axle instead of the more customary place on the gearbox. you didnt say whether you had a manual or auto box, but check both places, gearbox or axle, I think you will find that the electrical connections from the sensor to the speedo are either corroded or rotted, clean/replace these and the speedo should work.
Sorry this is a bit long-winded, but it could be either the VSS or the cables, you need to check both.

Hope this helps you,

Roy.