You can either follow the positive battery wire or just remember if your engine faces forward, the starter will be on the rear of the engine where the fly wheel is.
I think on your model it is on the lower right side of the engine. It would be best if you can get under the car while on a lift and just look up from the front of the engine and you will see a large round object that is horizontal to the floor and has a large battery cable attached to it. It is right at the point of the engine and transmission meeting. It is held on by two or three bolts. Be sure to disconnect the battery cables before starting to remove it.
It will be on your left from underneath the car and facing the rear. Sorry, didn't clarify that. Right side from drivers seat, left side from front of car.
Looking for a Used Thunderbird in your area?
CarGurus has 1,073 nationwide Thunderbird listings starting at $6,950.
Search Ford Thunderbird Questions
Ford Thunderbird Experts
Related Models For Sale
Used Cars For Sale