Problem with XPS3 turning on, and not off, but it's not noise...

[The Keeper]

It's entirely possible that the fixture is wired wrong such that the fixture is hot regardless of the position of the switch. Dangerous, but not surprising given the age of the wiring. I'm not sure if the NEC even existed when this fixture was wired up. None of the discrete conductors that are present in the box have a color anymore, and even if they did, there's no guarantee that the color was adhered to.

This living room fixture is part of the four original circuits in the house, and unfortunately, it's not likely that I'm going to be able to change anything unless I want to tear down the plaster and lath in a 9' living room ceiling to run new romex.

Guess I'm stuck with the XPDI3, but at least the reason for the failure has been identified.

Thanks,
Chris

[Noam]

If my diagram is correct, and if you can get to the wiring in the ceiling box, you should be able to test it out and probably fix it.

A length of wire, some clip leads, and a multimeter should be able to help you test the various conductors, and label both ends (with the power off, of course).

You should then be able to fix the wiring at both ends, so that the hot passes through the fixture box to the switch, and the switched hot is the one feeding the fixture.