I suppose you got your answer by now since your post was made in january or july (couldn't tell) - anyway, the keys for the mt-2500 scanner are for 1996 and newer vehicles - they fit in the obd II adapter and customize the different manufacturer specific pins in the 17-pin connector to work with the scantool. GM uses the K-9 key, fords use the K-2a and Chrysler uses the K-13 and the K-13a. I hope that helps. The tool will tell you what key to install when you enter the vin for every new vehicle you work on.
Jeff
