Believe you will find that the "small plug" is likely the round seal from the base of the antenna cable retainer that was used there. There is a smaller hole in the center where the opaque retainer sticks through as shown in the first picture. The bottom one shows two examples with the retainer/antenna removed but the seal remained. Most of the time it comes out when you yank the cable and retainer but not always on a Mustang/Shelby


Guess just another WAG or idea that faded quickly for the past owner.
An original tag or even original numbers on a rebody or a Dynocorn isn't better.




