Sight Unseen from Australia, it sounds like a Mantua Engine (Model Power engines are mostly self contained). The wire should be connected to the "coal car"-as-you-call-it/"tender"-to-me by a screw that holds the drawbar (piece of material that joins tender to engine onto the tender.
Turn your engine upside down, place the connecting drawbar over a spigot with a screw thread in to centre, find the retaining screw and place it in the thread. Wrap the wire around CLOCKWISE around the thread and tighten the screw. See if it works and if you are not sure, email me off list and I will take a photo of my own and resend it!
Regards
Trevor