I have a 2000 Ford Escot ZX2 and the speedometer stops sometimes. What do you think?

I have a 2000 Ford Escot ZX2 and the speedometer stops sometimes. What do you think? - 1

Does it drop to zero mph? If so replace the output shaft speed sensor. If it just sticks replace the instrument cluster

Thanks for your help Ben, and yes it does drop to zero mph. Where do I locate the output shaft speed sensor? Women don't know to much about repairing vehicles.