The light was out, the light was on; the light was out, the light was on. It was annoying. You've only read the cycle twice and I bet it's wearing on your nerves already. But finally, after almost three years of unpredicatability the light was out -- and wouldn't come back on. The light is in an exhaust fan in the ceiling in my master bathroom in my house in suburbia.
The fixture rattled intermittently; even after I had my builder come back and check it -- he just pushed it up a little so that the wedges on the edges gained some friction on the ceiling sheetrock. That lasted a few weeks. So we didn't use the fan much, but the light we used.
When it went out with no sign of coming back on I figured the bulb; a regular incandescent 60 watt light bulb, had blown. Testing it in my bedside lamp this proved to be the case. Replacing the bulb with a new one didn't help, though. The fan worked, the light didn't. (The fan and the light are separately switched.) Maybe the new bulb was bad, too? Okay, the exhaust fan is above the toilet -- a good place for it, except that you have to stand on the commode to reach the ceiling. It's a little short for comfort, but not bad the first time. But now it's the third time... (once to take the old bulb out, once to put the new bulb in and now a third time to take the new bulb out to test it someplace else, and of course that means a fourth time up in order to put the new bulb back in, assuming it works). Yes, it works; of course it works, it's a brand-spanking-new bulb fresh from GE. I put it back in the fan fixture: no dice.
Now what? Well, maybe the vibration of the fan loosened the wiring, or caused a short or something. So I broke out the step ladder, but it won't quite fit in the space where the toilet is, so it has to sit in front of the porcelain. A little better than standing on the toilet seat, but still an awkward reach. I removed the whole fixture, uncoupling the wire nuts and all -- but first I shut the circuit off at the fuse panel. Removing the fixture is a multi-step process: remove the plastic light cover, remove the light bulb, unscrew the cap nut from a bolt sticking down in the middle of the fixture (hey, the cap nut doesn't make the fixture fit snug against anything -- more on that later), then remove the fan grill and finally unwire the whole thing from the house. Oh, I had to go up into the attic to unwire the fan, couldn't reach it from the bathroom. So I had to crawl to the corner of the attic, careful not to hit my head on the nail points sticking down from through the roof, and reach across the open insulation and unscrew the fan wiring from its ground and wire nuts. Whew. (And just by the way, the "dryer duct" tubing on the back of the fan housing doesn't, as it should, vent over to the soffit under the eaves, it just exhausts the bathroom air up into the attic.... Oh, well.)
Conveniently, the light portion of the fixture actually plugs into the fan portion with a crude but standard sized plug. I put the bulb back in, plugged the light portion of the fixture into an extension cord and, voila, the light works fine. So it's something to do with the fan portion of the fixture -- or the wiring from the switches to the fixture, or....
So I break out my multi-tester and a spool of wire and start checking circuits. I open up the switch box and uncouple and recouple the switches, checking circuits as I go. I'm no electrician so I'm pretty grateful when I find that Lowe's has some nice online help for just my situation. I've got the "three wire with ground" case. But everything checks out. No electrical shorts, the switches close and open the circuits just like the diagrams say.
So maybe something was just loose. I guess I'll put it all back together and see what happens. Nada, that's what happens. Aaaargh. But I noticed, as I was screwing the fan fixture back into place that the bolt that the light portion screws onto, the one with the not snug cap nut, is just the shaft of a bolt, no head. This shaft is itself screwed into a piece of the fan housing. It's a set screw. Well, it may not have anything to do with my light problem (and it didn't, really), but at least the damn fan isn't going to rattle anymore. So I unscrewed the bulb, removed the cap nut, took down the light fixture (okay, I think I let it dangle by the cord plugged into the fan, so sue me) and adjusted the set screw so that the fixture was now snug against the ceiling and the cap nut was snug against the fixture.
This time as I screwed the bulb back in I paid more attention to the fact that the bulb was hitting the cap nut when it got nearly screwed in. I'd noticed this before but since the nut is metal there was no fire danger, but it was putting pressure on the bulb as I tightened it down. No different from before, but with my new knowledge of fans, wiring and set screws I think I had learned to learn about electrical fixtures. Anyway, even though a light bulb still didn't go on over my head, I had an idea: could the bulb just not be getting properly seated in the socket? Let's try a smaller bulb, shall we? I happened to have a couple dozen appliance size light bulbs (A15 size, I think they are) that I had ordered off the Internet. I stuck one of these puppies in the fan/light fixture in the ceiling in my bathroom in my house in suburbia and, ta-da, there was light. Yeah!
Now I'm wondering if the previous bulb had been an A19 and the new one I tried was an A21 or whether someone had just jammed the old one in enough to make good contact or what. I don't care enough to open the fixture back up and figure it out. I've got plenty of smaller bulbs, and I plan to use them.