Tonight I worked again on the electrical, found the short that had eluded us, fixed that, and then hooked up the fireplace. It has a circuit board off to the left, which controls three flickering lights that fit into a small acrylic fireplace insert. I can also hook up a set of 25 flickering Christmas lights to it!
I ordered a custom firebox from an Etsy vendor (Marquis Miniatures) that will hold the circuit box, and also cover the junction splice in the wall. Jill at Marquis Miniatures makes the most exquisite and detailed miniatures, and I enjoyed chatting with her today on the phone. Thank you, Jill!