It's probably not the wire, but it might be the connections. Do you have connectors on the ends of the wires (like banana plugs), or just bare wire? If it's bare wire, have you stripped it lately? You mentioned that the wire is old, and it might have become oxidized.
It probably is something else, though.
EDIT: If you have a meter, you could check the continuity of the wire. There should be very little resistance in the wire.