When I took out a permit to upgrade the knob-and-tube wiring on the main floor of my home, I had to figure out how to get the old wiring out of the plaster ceiling without removing a huge swath of ceiling to get at it. This is what I figured out:
- Remove old light fixture and open it up a bit, enough to install supports for the new fixture;
- Peering into the hole, determine the route the old wires took to get to the light, and hopefully spot one or both of the white ceramic knobs securing the wires;
- Measure from the hole to the first set of posts, then open up a slot in the ceiling -- just enough to get my hand and a screwdriver in there to unscrew the posts.
- Measure from that slot to the next set of posts and repeat.
- After all the old crap has been disconnected and removed, install new wiring.
- Keep ceiling open until after the wiring has passed inspection, then close each slot with a couple of pieces of new wooden lath (yes, you can still buy that stuff!), re-plaster, and paint.
