my speedo has stopped working what can cause it to stop working? and how do i fix it?

Sounds li=ke the Speedo sensor in the Transmission could be the culprit? They cost $60.00 new from Ford Dealers but you may be able to buy a cheaper one from a Wreckers or EBay?
They are the same all the way up to BF Falcons.

this happened to my car along with it goin into limp mode, the culprit was 2 worn gears inside the extension housing of the gearbox, theyre plastic n cost bugger all but to do it, you need a hoist (preferably) or engine stands!!!!! (dont forget to get another extension housing gasket!!!)

undolt the four bolts connecting the driveshaft to the diff n slide it out of the box carefully as to not damage the seal in the end of the housing. on the top right haand side of the housing, there will be a sensor connected to a wire, remove the retaining bracket to the sensor n then remove the sensor completely. support the transmission in someway fo safety and so it doesnt drop down to far and remove the support brackets underneath the ext housing to allow enough room for the mount bolts. remove extension housing (a little oit might come out) n there should be a gear visible around the shaft n one near the sensor port!!!!

try smurfs idea first as it is much easier to inspect!!!!

hope this helps

Im willing to bet the plastic cog in the speedo cluster has lost a couple of teeth.
Very very common. The cogs are available on Flea bay or wreckers.

By the way what on the speedo has stopped working?? The speed dial or the kilometers reading?
If its the speed dial refer to Papa's and Raptors comments, if its the Kilometers reading refer to my comment.

its all fixed now a mate of mine put in another cluster and fixed the problem of both the speedo needle and the gearbox problem.

So your mate replaced the dash and everything was fixed? My car's had a few problems after putting an EF dash in my EL, the speedo needle is flickering around, lately the car has been loosing its spark while im driving. Won't start for the rest of the day, but the next morning starts right up. Anyone got any ideas?