I installed one about a year ago and must say it was the best thing I ever did. Although it took me about 16 hours, I did it myself. If anything, I learned a lot about the jeep while installing it.

Anyway, did you put a jumper across the A and B pin of the ALDL connector and check to see what code if any was blinking from the "check engine" light that was installed.
Normally, you will get a code "12" blinking three times and then if any errors, will follow after that.