That is your cheapest option. Your computer has to be programmed with the particular key and ignition switch you are using. It's part of the Passive Anti-theft System (PATS) that your car is equipped with. You could buy a programmer ($399) to shut off the PATS but that is more expensive than letting Ford take care of it.
A forum community dedicated to Ford Mustang owners and enthusiasts. Come join the discussion about performance, builds, modifications, reviews, engine swaps, classifieds, troubleshooting, maintenance, and more!