I have a 3-way switch which lets me turn on the stairwell light from either the top of the steps or the bottom.
While building out the area around the downstairs switch I tied the switch with it's metal box and conduit off to the side and both switches worked just fine for months like that.
When I was done with the carpentry work, I pulled the light switch back and mounted it very close to where it was originally. Now, though, the switch at the top of the stairs always works but the switch at the bottom of the stairs only works if the one at the top of the stairs in the down position.
What happened? The house was built in the 50s, the wiring is in metal conduit and and has been given a clean bill of health by a wonderful electrician. Any ideas?