I have an old fixture in the Kitchen that needs to be replaced. It's a pull chain light on the old knob and tube system. The fixture and wires are so old they are not color coded. The new fixture has a white and a black wire. How do I know which is the Black wire on the two wires coming from the ceiling? One wire has a piece of black electrical tape attached to it so I assume it was put there to indicate the black wire, but I am not sure. What would happen if you mixed these wires up? Would it not work? Or would it work but have a greater risk of fire? Please help.