I am trying to install a progamable light switch in an older home. When I took the old switch out, all I found were two black wires and no sign of the whites...could they possibly be connected behind the box? I have lath and plaster and the box appears to be plastered into place, so taking it out will be a problem. I also have some knob and tubing wiring in that section of the house. I need a white wire in order for the new switch to work...any ideas?

Thanks