I recently changed a two prong outlet to a three prong. I am going to get GFI today and switch it out after reading online that it was not well advised just to replace the two prong outlet with 3 prong. I think when I hooked up the outlet I may have switched the hot wire and the neutral wire. Is this something that needs to be fixed immediately. Also how can I tell which wire is the hot wire. I assume it's the black one but the wires are old Knob and Tube so I am second guessing myself. Is it possible a black wire could be the neutral. Power should run regardless how its hooked up , even if I did switch the wires and incorrectly connect, right? Also why can't you replace 2 prong outlets with 3 Prong. What's the reasoning?