There is a joint in the door that joins the spare red wire you've got to the other red wire that goes into the door. They (or "it" in your case as one is not connected) feed both the electric mirrors (that's the connector with the violet wires in it) and the central locking motor (that's the connector that contains the white and yellow wires). I don't see a problem if you leave it disconnected, but wrap it in tape or heatshrink so it doesn't come into contact with earth.