Axman
Somewhat like you, I have 3 nests in trees. For a long time there were no takers. However, just last week we saw a House Wren going in and out of the one box with the most sun. Now, one of my bird book says that "Wrens often build numerous nests, which later serve as decoys or dummy nests for their would be enemies." And because the Wren that comes to this box is almost always carrying sticks, I suspect they are doing the decoy thing, and there are no babies.
But next year, I think I will move these boxes into more sunlight.