I tweeted this thread at @DeltaAssist, but they didn't tweet back

Based on some google searches and my limited knowledge of electrical engineering, I suspect that this is because on the 767, all of the lights over each "column" of seats (e.g. left side, middle, right side) are on a "party line", just two electrical wires. This is to save weight instead of having a dedicated wire from each seat to each passenger service unit.

When the controller wants to turn on light 17F, it says "command: turn on, target: 17F". But if the timer that synchronizes all of this gets out of sync, then the line is noisy and all of the lights get momentarily triggered.

To be honest, it would seem more likely that just a *few* wrong lights would turn on (assuming that this is implemented with some kind of counters). There must be some message for "all lights on", (probably a low number on the counter?), which is getting triggered by the clock drift.

So while it's insanity inducing, it's probably not a safety of flight issue.*

Based on some discussion on other forums, it sounds like the problem is tracking down the counters that are drifting is very hard to do, because when the plane is one ground power, this problem tends not to manifest itself (although that discussion was about an airbus, I'm willing to believe that the issue is similar).

*Either that or we're about to have another swisair, as someone up thread mentioned.