Which court case or legal action brought the fourteenth and fifteenth amendments back to life?

Guinn v. the United States in 1915. The case was fought because an amendment to the Constitution stated that a person in order to vote had to satisfy a literacy test. If they didn't then they could still vote if their grandfather had been a voter. This meant that African Americans, if illiterate could not vote due to their grandfathers not having the right to.