Check the back of the speedo then or the speed sensor i think its called Ram 360 had a speedo not working and he changed that part and it worked fine..
There is a sensor that holds the speedo cable in place if it goes bad along with the gear it will make the car read faster or slower and make the needle bounce.. I had the bounce problem in my 87 and i changed the thing and it stopped.
Far from both of them there my friend. And this same topic will come up again in the next month just because you dont speed does not mean other people do not..
Which person would i be then? And no this comes up every school year some kid in a 5.0 complaining he isnt speeding but he gets pulled over or gets yelled at.. Its the same stuff different day.
What im saying is he is probabbly speeding and thinks he is cool doing it because he has a mustang and then when somebody stops him on it he gets all offended. Ive been hanging around here for a bit now and read a lot of threads by now i wouldnt doubt it.
I beleive he said he only wanted to change the dash. That can be done without cutting wires.. You just have to swap the connectors out on the harnesses. And 86 is already EFI