Fuse links are inside the wiring harness that runs form the starter solenoid to the fuse panel and ignition switch. I don't have a diagram for an 82 Mustang, but I will post one for later models; they should be similar.
Fuse links come with a current rating just like fuses. A clue as to what current they are designed for is to look at the size wire they protect.
Fuse link material is available at most good auto parts stores. There may even be a fuse link already made up specifically for your car. Just be sure to solder the connection and cover it with heat shrink tubing.
Heat shrink tubing is available at Radio Shack or other electronics supply stores.
See the video below for help on soldering and heat shrinking wiring. There is a lot of useful help and hints if you don’t do automotive electrical work all the time.
View: http://youtu.be/uaYdCRjDr4A
For free automotive electrical training, see
Automotive Training and Resource Site . I have personally reviewed the material and it is very good.