What would be wrong with the turn signals in a 1991 Thunderbird if it is not the fuse?
What is it doing or not doing? In my 91 thunderbird my drivers side rear blinker has a short, if I wiggle the wire then the light works for a couple of weeks, probly a bad ground. Check the flasher in the fuse box, It is usally round. If that checks out you may to check the turn signal switch in the steering colmun.