To be certain, you should:
* Consult your owner's manual: This is the best source for the precise location.
* Look for a large black box with numerous wiring harnesses connected: This is the most likely candidate.
* Search online for a 1992 Ford Aerostar engine bay diagram: A visual diagram will help you locate it.
Remember to be careful when working near the engine bay and disconnect the negative battery terminal before doing any work on electrical components.