I had an old (1976) GE electric cooktop that I'm replacing with a new Whirlpool. The GE had 3 wires, red, green and a copper wire. The new Whirlpool has 3 red, green and black. The connection box has four wires coming out two black, one grey, and one un-insalated metal wire I marked the red & green wires with tape to tell the differance please advise Please. Thank you in advance.