I´m sure you solved this by now, but just in case I wanted to share a similar problem and solution. I bought a 2000 Tbird about 6 months and it wouldn´t start in gear (only neutral). After a while didn´t want to star at all. I fixed this by removing the clutch switch (tiny plastic device on the clutch master cylinder) and cleaning off the contact points with a qtip soap and water. Starts perfectly now. Try that if still not working. Plenty of YouTube videos to explain. Good luck.