Hi sometime the Odomiter on my 95 continental stick
and then sometime it decied to start flying all around what could couse this

I have had speedometers jump around because of broken or worn teeth on the gears.....if it is an electronic pickup in the transmission, I guess it could be a bad sensor. They may use a halleffect type sensor to pick up a rotating magnet in the transmission or something like that. Maybe a bad connection in a plug?