How do car speedometers work?
the ones now days work off a speed sensor that mounts in the transmission,and sends a signal to the computer and this also travels to the speedometer head and it has a small motor in it that turns the speedometer,there more complicated than the use to be,all they use to have was a cable that ran from the transmission,up to the speedometer,and this turned everything,now its all computer controlled,good luck ,hope this helps.