from The Craft of the Cocktail
Ice a highball glass. Add the tequila, pour in fresh orange juice, and top off with a float of grenadine.
The original Tequila Sunrise appears in cocktail books in the 1940s and is made with sweetened fresh lemon juice instead of orange juice, and cassis instead of grenadine. (I found that recipe in The Roving Bartender by Bill Kelly, 1946.)