To find it precisely, you should:
* Consult your owner's manual: This is the best resource, as it will have a diagram showing the location.
* Check online forums: Search for "[your specific Nissan truck model] ECU location" on forums like NissanForums.com. Pictures from other owners are extremely helpful.
* Look near the battery: It's often near the battery or other electrical components.
* Look in areas with easy access to wiring harnesses: The ECU needs to communicate with numerous sensors and components.
Without knowing the exact model of your 1994 Nissan truck, a more precise location can't be given.