My speedometer was not working and I had a check engine light with a code for speed sensor. I replaced the speed sensor and that did nothing. Then found that I had a speed calibrator installed in the car. I contacted Dallas Mustang who's name was written on the calibrator box, they told me the speed calibrator went bad. Well, I spent the $120 and received a new one, installed it, and my speedometer still does not work. What is my problem. And yes all of my wires are hooked up correctly.

 

We need more info like what year mustang do you have?

 

Sounds like a wiring problem (i.e. bad conection or broken wire)