[broadgage]

Fairly low tech memories in my case, mainly locating the failed bulb in a series string.
At a young age I was sent to various neighbours to "get the Christmas lights working"

I recall some people having home made Christmas lights that used pilot lamps in series because they could obtain these from work, rather than buying proper Christmas light bulbs.

40 lamps in series, each a 6 volt 0.3 amp panel lamp was popular. These could be coloured by dipping in lacquer sold for the purpose. Finding the failed lamp out of 40 was a lot worse than with 12 series lamps.

My uncle, who had previously owned a radio and electrical shop, had Christmas lights that consisted of numerous 120 volt, 15 watt candle bulbs in series pairs, because he was stuck with a surplus of these.

I also remember bright metal plated Christmas decorations that were intended to hang over a light and rotate in the warm air current, the rotation was intended to play a tune as the rotating part struck minute bells or chimes. They never worked very well, and in retrospect I suspect that they were intended for use with gas or oil lamps, not electric.
(similar novelties are still made today, but to stand on a table and rotate in the hot air from candles)