Hi, Dave
Sounds like you have a 25 pin serial cable, What you need is a straight through printer "extender" cable, 1-1, 2-2, 3-3 ...25-25, Some cables omit some of the 18 - 25 Gnd. wires, But this shouldn't be a Issue, Gecko is probably smart enough to have them all tied together in there box.
Thy come in two versions, 25 pin M / F and F / F connector's, The F / F you'll need a gender changer M / M adapter.
Chip