In the Break of Dawn Daedric quest for Merida, one traverses Kilkreath Ruins finally coming to a locked door that can't be lock picked. There is no key in the dungeon or clue to where it might be.

The guide (searched in frustration) says to get to the Word Wall behind the door: "Area is locked (quest required)" but does not tell what quest or how to find out.

Has anyone solved this mystery?

You need to activate all pedestals - when light reaches the central orb, the door will open.

No. Not that door. The door behind the altar after you pick up Dawnbreaker.