Are you sure they are the right size? What happens when you put them in? Are they not going in far enough for you to twist and lock them in place? If so, try pulling up on the wire. The sockets are spring loaded, so if you pull on wire then you are compressing the spring making it easier to get the bulb in.
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!