This cable is used to program ECT modules using a PC with an inexpensive USB-to-serial adapter. Programming is only needed if the standard ECT module programming is not a good match for your car or if you want to change the way your temperature gauge is operating. Detailed programming and troubleshooting documents are available in the Manuals tab here and on the ECT Module product page.
NOTE - Make sure you buy the correct cable. If your ECT module has a plug-in connector then you need to buy the Cable for Original ECT. If your module has screw terminals buy the one for "current" ECT modules, or you can make your own using the instructions in the Manuals tab.
ECT-2 Programming Instructions PDF help file
Make your own programming cable (Screw-terminal ECT modules only) In case you don't want to buy ours
Below are short videos that will be helpful if you're going to be re-programming your ECT module.
The first video was made while installing a USB to Serial converter and the second shows how to set up a Generic Text Printer on your PC.