1989 Cadillac Brougham

Computer problem
1989 Cadillac Brougham V8 Two Wheel Drive Automatic 66000 miles

I have a 1989 Cadillac Brougham, and it wasn't driven very often for about three years. I just had a tune-up done, and the check engine light is still on there. I work at a Chrysler dealership, and the mechanic has a GM connector to see where the problem might be. He wasn't sure if the Cadillac had a connector like they use (he said he knows that at least in 1994 they used what they use now.) Short of spending alot of money for his diagnostic fee, is there a connector that could work?
December 3, 2008.

Disconnect battery or pull ECM fuse for 30 sec code will be erased then drive if no light O.K. Light back on connector under dash near ash tray plug. If he has an OBDI plug in read

Dec 3, 2008.