Combine sugar, syrup, sour cream, butter, and salt in a medium- size heavy saucepan; cook over medium heat, stirring constantly, until sugar dissolves. Cover and continue to cook over medium heat 2 to 3 minutes to wash down sugar crystals from sides of pan. Uncover and cook, without stirring, until mixture reaches soft ball stage (236°).
Remove from heat, and let stand, without stirring, 15 minutes or until mixture cools to lukewarm (110°). Add vanilla, chopped pecans, and cherries; beat with a wooden spoon until mixture thickens and begins to lose its gloss. Working rapidly, spread mixture in a buttered 8- inch square baking pan. Mark top of warm candy into 1-inch squares, using a sharp knife. Cool completely before cutting into squares. Store in airtight containers in a cool place.