To find it, you should:
1. Consult your owner's manual: This is the best resource. It will have a diagram showing the fuse box location and a legend identifying which fuse controls the taillights.
2. Look in the fuse box under the hood: Many Chevrolets have a fuse box under the hood, often near the battery. This box typically has a cover with a diagram indicating which fuse is which.
3. Look in the fuse box inside the cab (if applicable): Some models also have a smaller fuse panel inside the passenger compartment, usually located under the dashboard.
4. Look for a fuse labeled "Tail," "Tail Lamps," "Stop Lamps," or a similar designation: The fuse for the taillights might be combined with brake lights, so check labels carefully.
Without knowing the exact model of your 1994 Chevy pickup, I cannot provide a more precise location. Referencing your owner's manual is crucial.