Greetings from Fresno California, where we have a 1920's or 30's house that I have started to rewire. I will have other projects with the house but the rewiring takes priority now. I will give some updates and ask questions in the electrical forum as I go along.
For entertainment purposes only, I will describe a few of the issues which convinced me to do a rewire.
Not long after getting the house, my wife buys a new different back porch light. I remove the old fixture and see that there is no box, only two wires potruding from a hole in the stucco. (Its an old house, to be expected). I turn the power back on to see which wire is hot. Mark that wire. Turn the switch off...... doulble check voltage in the wires. Both wires now have 120 V. Turn the switch on; one wire has 120 v. Turn switch off, both wires have 120 V. Do this a couple times as I have to convince myself. Look at wall and roof line and wonder how bad it will be to fish new wire to this location.
A bathroom light quits working. My noncontact volt detector picks up voltage everywhere in the bathroom. I'm freaking, but a check of the actual voltage shows low voltage. There is 120 v to the switch itself. There is new nm cable to the switch and light, but in the attic, I find knob and tube going into the wall. I cuss at unknown persons for awhile. I trace wires and think I may have found a problem in a loose wire, but I am really puzzled and am reluctant to connect it. I bring up an electrician, he checks a few things connects the loose wire into the neutral circuit and the bathroom light works again. But I am puzzled. That wire had been disconnected sometime in the past (not just a loose connection) and the light had been somehow working for some time. Weird.
An outlet in the bedroom adjacent to the same bathroom has a bad outlet; no ground, 120 v with no load, but almost zero volts when a load is applied. Obviously a bad connection on the power or neutral. My testing indicated the bad connection was on the power side. I figure I'll bring in some pros. These electricians trace out the knob and tube to that outlet and decide that there is a loose neutral. The fasten it securely and the outlet works again. They claim that the wiring updates in the attic are the worst they have ever seen. I new it was bad and "worst" didn't surprise me. The electrician says it needs a complete rewiring job at around $8,000 and they could get to it in the fall when it is cool enough to work all day in the attic. He also suggests that we cut the walls where the wires need to go so they don't waste their time doing that. Oh, and hire somebody to remove all the blow-in insulation so they can see where the wires go. Good idea actually.
Two months later, the outlet quits working and the bathroom lights and fan quit working. A day or so later, they work for awhile in the afternoon, but quit working again in the evening. Photocell??? A few days later, they work again for a few hours in the afternoon, then didn't work for several days. I get in the habit of checking to see if they work and one evening notice that two outside lights come on when I turn on either the shower light or the shower vent fan.
I like puzzles, and someday I will figure out a circuit that will cause these effects, but in the meantime, I went into the attic and cut all the knob and tube wires above the master bedroom that connect those fixtures. I have started running new wires and putting in new boxes and will put them on a new circuit. I figure no electrician on the clock has the time to fix this mess in a reasonable way. Where I have the time to work on it one circuit at a time, run new wires replace every nongrounded box and make it all neat and logical so the next guy can see what it going on. While at it I can work on various other problems as well. And I can work on it for a few hours at a time when the attic is cool.