If I Have Two Black Electrical Wires, How Can I Tell Which The United States has strict codes relating to home wiring, including clearly defined colors on the outer casing of the wires. Black means hot, white signifies neutral, and green indicates ground. However, if you need to rewire a light switch or a plug socket, you may occasionally come across two black wires. History of Old electrical wiring identification: photo guide Photo guide to types of old building electrical wires. These photos help identify types, condition, & hazards of old electrical wiring in buildings. In this article series we list common old building electrical wiring system safety concerns and we illustrate types of old electrical wires and devices.