If the third wire is a bare braided wire, that was an outer shield to keep out electrical interference. That would just have been wrapped around the other two wires, and wasn't connected to anything.
If that third wire is a regular wire, especially if it has a single connector on the end, that is likely for an option that was never installed on your car. They include that so it is there for those cars on the assembly line that do use it. Your car will be full of similar unused connectors like that.
Wednesday, May 3rd, 2017 AT 1:20 PM