(answer not needed fast)
So I’ve got the lights on the tree after much effort. A large part of this effort was due to the fact that I found out one of the strands (that I had plugged in a few days ago and checked out fine) was not working, after I’d gotten it wound up in the tree.
This strand was malfunctioning in a specific way that I’ve seen before - it was out at the halfway point, rather than the whole strand being out. These are newish strands, and can tolerate one or more bulbs being burned out, and still function. In fact, the problem strand had several bulbs out in the first half, which I replaced, but it still didn’t help.
What exactly is going on here? And considering that Christmas lights are about one of the simplest electrical circuits one can imagine, how the hell can they suffer from such aggravating, difficult to diagnose problems?