Ford Repair Questions? Ask a Mechanic for Answers ASAP
I'm assuming your husband's mustang has a manual transmission as replacement shift knobs are typical found for manual transmission cars and aren't always offered for automatics. With the manual transmission the shift knob simply unscrews light a light bulb and the new one screws right on, it may be fairly tight but don't worry it will unscrew.
I hope I've been able to answer your question, if you have any other questions or if you would like more information on your current question please feel free to ask.