There was a mid year change to an exterior 30A , as you already know.
The fuse mod was simply put in parellel with fuse 12 [ 25A]
You have to get to the bottom side of the fuse panel #12, where you will most likely see the wires burnt. If you can clean the feed wire back , hook a new exterior fuse to this feed and splice the other end into the red wire . That will give you fuse protection and feed only when key is ON.
Use heavy stranded copper.
That's it.