where is the aldl or obd connector in a 1990 cadillac allante?

Too old to have one. You will need to get an older diagnostic tool or learn to read the trouble light codes those cars were built with. Also, the level of sophistication is way below what current diagnostics are.

I disagree with the previous answer. GM started putting an ALDL (Assembly Line Diagnostic Link) on vehicles in Mid-1980. To some, it is also referred to as the OBD-1 connector. My research has indicated the Allante' ALDL was located Near the Emergency Brake pedal....behind an access cover. I believe Cadillac was also the only GM car line to have its own On Board Diagnostics....which was accessed through the HVAC controller by pressing certain buttons. Research will explain how to use this Helpful feature.