David,
https://www.sbig.com/site/assets/fil...ing_manual.pdf
Go to page 67 and make your own that connects to 12 volt source. It's only a DIN plug. A soldering iron, 1 DIN Plug, a bit of wire. Get a friend to help.
SBIG offer no assistance on procuring bits for the older stuff. Pity really. It's a nice camera. Their response, try astromart. Great support to those that have existing equipment.
Terry