To be certain, you should:
* Consult your owner's manual: This is the best source for the exact location of your vehicle's ECM.
* Check a repair manual specific to your 1988 Buick Riviera: These manuals usually have detailed diagrams showing the location of all major components.
* Look for a large, rectangular black box with numerous connectors: The ECM is usually a fairly substantial electronic component.
Be cautious when working near the ECM as it is a sensitive electronic component.