I just finished replacing the thermostats and elements on my Rheem hot water heater. The insulation on the main black wire feed at the top thermostat was corroded for a couple of inches - long enough back that I couldn't use slack wire. I took the electrical junction box apart with the idea of replacing the wire, but both the black and red wires look to be somehow foamed in or otherwise difficult to remove/ replace. Is there a trick here or do I need to call an electrician? The wire still appears to be in reasonable shape. Could I get away with wrapping some electrical tape around the exposed copper?