To be sure, it's best to:
1. Consult your owner's manual: This is the most reliable source for the specific location in your truck.
2. Look carefully under the driver's side dash: It's often near the fuse box or other electrical components. It's usually a small, square or rectangular box with a button.
3. Search online: A Google search for "[your specific 1998 Dodge truck model] inertia switch location" might yield images or forum discussions showing its precise location.
If you can't find it after searching these places, a qualified mechanic should be able to locate it quickly.