If you have cruise control, you can disconnect the cable going to the speedometer at the transducer in the motor compartment and have some watch as you spin the cable by hand to see if the needle moves. Then you can pull the bottom cable and check for problems there. It might be in the transducer, but usually not, but still could be. If spinning the cable doestn't move the needle, it could be in the head, but you would need to also check this smaller cable. To do both would require getting behind the dash. I hope it is the lower cable or a gear in the transmission(easier to get to). Anyway good luck with your work.