Quoted from DropTarget:I'm a bit confused, looking at the picture in post #15, I see the jumper across the + terminals, but it looks like both sides of the battery holder go to - terminals. Could you clarify?
Clay is right that the picture is self explanatory if you're looking for a cookbook explanation.
If you want to know why it works, it's important to know that the 3 AA batteries are in series with traces on the board to connect them.