If the fuel computer is on instant econ and the numbers are anything other than zero then the sesnor must be working. But the speedo is never going to work without the cable connected up.

This is getting very confusing because the standard Escort RST gearbox came with an LSD - you don't need to fit one. It's possible someone's changed the gearbox to an MTX75 but even so I think the speedo should still connect up OK.

I just can't see the problem - the cable you bought should attach to the clocks at one end at screw into the electric sensor at the other. If you look at the sensor you should see there is a hole in the top for the speedo cable to go into.

Can't you post some pics up beacuse something is not right here