Oh, no, didn't make it up myself, although it could be said my sources were dubious. It interests me, too, and I plan to follow up on it later in the day. In the meantime:
essenechristianity.com/taurus_the_bull.htm
the-red-thread.net/God-of-Taurus.html
nexxushost.com/szurane/taurus/horus.html
ETA: Don't know why the links weren't parsed, sorry about that. They still work, though if you copy/paste them into the browser.
According to Budge, the Name 'Horus, the Bull of Heaven' [Hor-Ka-Pet] referred to the planet Saturn, not the sign Taurus, and was represented by a Bull-headed Hawk. (Mars was Hor-Tesher, Red Horus, and Har-Akhti, Horus of the two horizons, Venus as Morning Star was Horus of the Tuat, Horus of the underworld, and was the ferryman of Osiris).
(Although much of which Budge wrote is wrong in terms of modern scholarship, he was perhaps of some influence of the Egyptian concepts of Aleister Crowley (several of his books were published pre-cairo working) and perhaps other Golden Dawn members though the publication of the Book of the Dead, 1895 is a little late for that; the Golden Dawn God name conventions suggests a French or German source, rather than English.)
According to Jane Sellers
The Death of Gods in Ancient Egypt, 2007: "...there is seemingly no correlation... between Horus the Bull of Heaven, and our constellation, Taurus." She also says that 'Horus, the Bull of Heaven' was a title of the Planet Saturn in the 18th dynasty. This is also confirmed by several modern texts on Egyptology (the constellation of the 'big dipper' was also called the bull or 'the bull's penis'.
Horus, the Bull of Heaven as the name of the planet Saturn can also be found in several 19th century German and French texts, for example,
Ueber die [epaphrodisia] und den Symbolismus der Zahl 30 in den Hieroglyphen by Heinrich Karl Brugsch, 1855, whose brother, fellow Egyptologist Emile, assisted Crowley by having his assistant translate the Stele of Revealing in 1904.
Samuel Mathers was also familiar with the works of Heinrich Karl Brugsch (he quotes from him). Works of Brugsch are also quoted in the minutes of the Ars quatorum Coronati, of which Mathers and Westcott were members, by co-founder of the G.D. William Robert Woodman (in a review of Westcott's Isiac Tablet of Bembo).
The hierophant/horus conflated with taurus (the bull) = Horus, the bull of heaven = saturn/satan? (the something sinister about this card!?)
"Ο -- The exalted “Devil” (also the other secret Eye) by the formula of the Initiation of Horus elsewhere described in detail. This “Devil” is called Satan or Shaitan, and regarded with horror by people who are ignorant of his formula, and, imagining themselves to be evil, accuse Nature herself of their own phantasmal crime. Satan is Saturn, Set, Abrasax, Adad, Adonis, Attis, Adam, Adonai, etc...."