Preliminary note: if you're not sure about a circuit, be safe and turn off power by tripping the breaker.
I'm not an electrician either, but I do know how to do things in a manner which won't kill me or the next guy. The P.O. in our case wasn't an electrician, and he sure as hell didn't know how to do electrical work properly (my first clue was the half-ass wiring for the ceiling fan/light in the kitchen). This time, it's the basement wiring which was added at least 20 years ago to provide additional light to the basement, back when they used to have a bar down there. It was done with a combination of rigid and flexible conduit, and on the surface it looked OK - no visible wires, conduit clamped to the plug boxes, etc. Both lights I was changing out were old, crappy, and hardwired so they needed to be removed and replaced with grounded outlets so I could plug in some generic fluorescent tube fixtures. The basement is only used for storage and laundry, so fluorescent tubes are good enough for now.
Once I started taking things apart is when I found what kind of half-ass job was done. Typically on a switched outlet, if you flip the switch to the "off" position it breaks the circuit's black/hot wire and the fixture is dead because power can't get to the fixture. I'll usually work down-stream from the switch like this in relative safety (I'm dealing mainly with very simple circuits in this case, and if I'm in doubt or if I'm replacing the switch itself I kill power at the breaker). In this case, the P.O. put the switch controlling the light on the white/neutral line instead of the black/hot, so even with the switch off live power was still going to the crappy old hardwired light I was removing. Normally this is easily found ahead of time, but the light fixture I was removing was a 1' x 2' pool table light which was screwed directly to the floor joists with an electrical box screwed to it's top. I removed the screws holding the light to the joists and as I was lowering the light I decided to pull the circuit tester from my back pocket to check things out, since I didn't know what was hiding in the conduit (my circuit tester doesn't read power if the wires are in the conduit - it only registers power when the wires are exposed). Lucky for me I did check it before starting to remove the electrical box screwed to the light and found out it was live, or I could have easily become the circuit's ground. To make it more fun, the P.O. did a crappy job using flexible conduit for this run. There was not a solid ground from the flexible conduit to the electrical box, so he wrapped a length of copper wire around the conduit and ran it through the screw holes on the box. Yeah, that'll work.
The last fcuk-up in wiring by the P.O. was that he used way too much flexible conduit. I've got about 2' too much line flopping around between the open studs. Oh yeah, it's not secured to the studs either, or I wouldn't care quite as much about having too much conduit. Tomorrow I'll have to stop out and get some clamps to secure the conduit to the studs.
Holy Half-Ass Wiring Job, Batman!
Long story short, I killed power at the breaker and replaced the old switch and re-wired the circuit so that power is cut on the black/hot instead of the white/neutral. The fixture was replaced with a new single-gang box and grounded plug, properly set up to connect to the flexible conduit. As much excess conduit as possible was removed from the line to clean things up. I went from having three small light fixtures in the basement to having five generic shop-type dual-bulb fluorescent tubes. Now that I've got good lighting I have noticed a number of other "interesting" electrical adventures in my future. Since the old bar was ripped out long ago I am guessing a number of the old circuits down there could be removed to clean things up a bit. I haven't checked code, but I would think that the water pump should be on a dedicated circuit and not have three other outlets on the line with it...
The funny thing is that our house passed an electrical inspection done by the city before we could take ownership. These problems weren't super obvious (like the hardwired 220 line for the stove done in an even more half-ass manner - more on that when I get to that part of the kitchen renovation) but should have been noticed if they were serious about the inspection.
Moral of the story: just because the P.O.'s work looks OK, don't trust it until you check it yourself. You're P.O. might have flunked Electrical 101.