I have answers to a couple of your questions Delidog.
Marguerite Henry wrote great books such as Justin Morgan had a Horse and the Misty of Chincoteague series of books.
I loved Black Beauty, I remember two of his horse friends were Ginger a chestnut mare (Ginger Snaps! because she bites) and little Merrylegs the old grey pony!
Was the song about a racehorse called "Wildfire"?
I'm also thinking about that song by America called "A Horse With no Name" but I know that isn't the one.