This has a factual answer, so I think GQ is the correct place.
A single-pole light switch needs to be replaced in my house. It has 3 wires: 2 for power, and 1 for ground. I marked the ground wire so I wouldn’t mistake it. The other 2 wires are black and red. Of course, I had to remove the switch to take it to the hardware store to buy the correct replacement…
Like an idiot, I didn’t mark whether the black wire came out of the “top” hole in the switch or the bottom hole. (The switch orientation: assume I’m holding the switch in an upright position, like it would be if it was already screwed into the wall. When the switch reads “off”, the switch is pointing down, like it would be if it were in the wall.)
My question: does the red or black wire go in the top hole?
Also, what should I expect to happen if I get the orientation wrong, and I turn on the power?