To please a couple of the more pedantic characters in this thread, in the interest of full disclosure I thought I'd explain how it is I am hardly inexperienced.
I am installing a light fixture. When I took the old light fixture off I noticed in the ceiling that there was a black wire that came in and was tied to another black wire that continued the run. From my DC days I know the black wire to be ground, so I spliced into it and attached the light's green wire.
I think the fixture is faulty because when I connected it's white wire to the white wire in the ceiling I felt a little funny. But my circuit breaker is also faulty because it threw right away. Downstairs I couldn't get the breaker to stay in one position, it was that worn, so I put a self-tapping screw direction through the top of the switch to hold in the on position.
Light works! But buzzes & flickers horribly. Lots of noise in the breaker box too. I'm blaming the switch upstairs....it's the only thing left. I know that it isn't a 3 way switch because it only goes two positions, so I'm not quite sure what is going on here. I can't even guess what the red wire up there is for.
There's always some wire left behind in all my installations....you know how it is.