I got this from a friend today. He says his father had it from the 70s.
It doesn't look familiar to me at all!

 

pinto`s also used the running pony but i cant find that on one

 

If I remember correctly, a buddy of mine in high school had a mid 80's four cylinder mustang. It seems like those may have been on his car. Going back almost 20 years so it is kind of fuzzy.

 

I feel confident that I have never seen a Ford factory wheel cover like that.

What size (diameter) is the wheel cover? Is it plastic or stainless steel? On the back of the wheel cover, I would look for the Ford logo or FoMoCo logo to see if it is a genuine Ford part or accessory. If it has a Ford part number, write it down and post it. Ford part numbers usually have the first and second characters indicating the first year of use. If no Ford markings or partnumbers then this is from some aftermarket manufacturer.

Ford's factory wire wheel covers always had genuine wire spokes. Another clue is the running pony design. The pony was changed according to which generation Mustang it appeared on. I will say that most factory wire wheel covers did not have pony emblems but rather generic emblems or center caps which were shared with other Ford models.

Here is a good link that shows all factory wheel covers for Mustangs.

http://www.hubcaps.org/mustang.html