If on the other hand, the wire comes from one of those locations, or a plug type connector seperate from the power cord, it should attatch to the loop antenna.
If yours is one with FM too, check the FM reception, and if that is weak, it is possible that this wire came off from a metal tab that wrapped partially around the power cord- It would use the power cord as the FM antenna, but it would rely on the insulation of the power cord to form a capacitive link between the two.
: I have a loose red wire and can not see where it has come from, the wiring diagram is missing,simple instructions suitable for novice please.