I have a situation where a number of wall sockets have gone dead and one of them is indicating voltage on a Non-Contact Voltage Tester but when I plug in my 3-Wire Circuit Analyzer Voltage Tester nothing lights up which should indicate that there is an open hot. The rest of the sockets give no indication on either meter.

To give some background, I've been helping a friend who had had some electrical work done when they had a ceiling put in in a room in their basement. The electrics in the house are 40-50 years old, reliant on a fuse box, and have been DIY modified by the previous owner.

The person who did the most recent work didn't really finish the job and made several mistakes after which he put up a drywall ceiling, closing off most access to the wiring. The end result of his work was that a wall socket in the basement was not working and the ceiling light at the far end of the basement was permanently on while the light closest to the stairs was controlled by a switch at the top of the stairs.

I pulled the fuse and took the switched light off the ceiling and found that there was a 2 hot 1 neutral wire carrying current into the box. The red wire was attached to the switch and the black was uninterrupted current. The hot leading to the broken wall socket was attacked to the black... and so was the neutral leading to the wall socket so that wasn't hard to fix. The wire leading to the other light was also attached to the uninterrupted current and I moved that over to the red (switched). The remaining wire in the box was a mystery so I wire nutted it off for the time being and left it.

Once I was done I put the fuse back and the basement was now wired to my friends liking, but we found that there was now a dead socket in the living room above. I realized that was the mystery wire so I went back down and attached that to the uninterrupted circuit, went back up and found it was working. However, at the same time, a number of sockets in the kitchen and dining room went out.

They are on the same fuse, but for the life of me, I can't figure out why they aren't working because there are no more loose wires. They WERE working when the one in the living room was out and the only change I made was to attach that to the one loose wire that feeds the living room socket. The other strange change is the one socket in the kitchen which is having the problems I described above.

If anyone has any idea what could be causing this please clue me in.