check fuse panel
I would check the fuses first. It may sound stupid, but it the easiest thing to check first. I was once working on a 95' Honda Accord and I blew the ECU fuse (dont ask how) and I didn't know that it had blown until I started the car and it would not shift out of park. Just before I was going to have it towed to a dealer, I checked the fuse box and sure enough, the 5 amp fuse was blown. The same may be true for a Tbird, but not sure. Hope this helps.