I went to replace an old baseboard heater. The black wire was black instead of copper colored. Sounds like this is not right. What could it be, and do I have to replace the whole wire inside the wall. Was wondering if this could have been caused by one of the two heater wires (connected together behind the other plate in the opposite end of the heater)- coming out of the mar connector and touching the metal casing of the heater.
PS-my question under LAW category was not mine---was for a friend.

The copper wire may have been blackened by heat due to a loose connection. If this is the case, the wire is not so important as the insulation. Check to be sure the insulation is not damaged by heat, such as cracking or is brittle.

Any wire with damaged insulation may need to be replaced, or covered with electrical tape. If the damage extends beyond the heater into the wall, the cable may need to be replaced.

The black coloring on the wire itself can be scraped or sanded off to clean the wire and insure a good connection.