I was switching out some incandescent bulbs for Cree LEDs in a multi-socket light fixture for a friend recently and ran into something odd: the LED bulbs wouldn't turn off at the light switch, only go dim. When it was 100% incandescents, the incandescents appeared to be off when the switch was off, but 100% LEDs simply will not turn off. If you combined an LED with an incandescent, the LED would go off as well.
I checked the wiring, here's what I've got, and it's all reasonably modern 3-strand (neutral/hot/ground) TPS cable. On the north side of the ceiling box (coming from the light switch and breaker box side), there's two sets of wiring coming in. On the south side, one set of wires. The circuit powering the ceiling light also powers all the wall outlets in the room, and I'm unsure of where the south side wiring extends off to in the ceiling, but I suspect the back porch light if I were to take a guess. I also haven't undone all the wiring to figure out which run specifically goes to the wall switch for this ceiling light.
Right now, here's how it's wired. For the sake of perspective and understanding looking up into the box, we'll label the northwest wire run (1), the northeast wire run (2), and the south run (3).
-(1) black/hot wire is connected to the light fixture.
-(1) white/neutral wire is connected to the black/hot wires on (2) and (3).
-white/neutral wires on (2) and (3) are tied together and connected to the light fixture.
-ground from (1), (2) and (3) are all tied together in the box.
I figure (1) is the run to the light switch.
The multimeter still registers the fixture wiring as hot even in the off switch position (obviously), but it's clearly got some resistance in the line and isn't anywhere near full power. A part of me also wants to say from what I understand of electrical wiring, the wiring looks right to me for what's being done, but I am not an electrician. After sleeping on it and typing this out, I'm starting to suspect my initial gut feeling that the wall switch is failing is probably correct, but I'd like a second and third opinion on the wiring and situation before trying to swap it out as it's buried behind a 1/4" sheet of well adhered fiberboard backsplash that only had the minimal amount of cutting out done for the light switch to poke through and get the cover screwed in.
So, could it be screwy wiring or just a faulty/failing switch?
Photo attached of the ceiling box. Thanks in advance!