I think I know about where the other end of the 3 way switch is.
Outside just below the light (that is connected to the switch inside) is a GFI Switch that is also not working. I suspect the switch I am trying to connect also is tied into the GFI (outside). So inside my house is a 3way switch and just outside on the other side of the wall is a light, just below the light about 4 feet is a GFI. Both the GFI and the light are not working.