A red wire in an electrical outlet often indicates a second positive live wire. Generally, electrical socket boxes come with three wires, each of them colored differently: a live black wire, a green or copper ground wire, and a neutral white wire.
In most cases, a red wire present in an electrical outlet means that a switch can operate the outlet. When the switch is in the "on" position, the red wire supplies power to the outlet instead of the black wire. Sometimes, a box wired for 240 volts instead of 120 volts has both a black and red live wires.