The inertia switch on a 1984 Ford Ranger is typically located
under the dash, on the driver's side. However, its exact location can vary slightly depending on the specific trim level and body style. It's often near the fuse box or other electrical components. You might need a flashlight to see it clearly.
It's a small, usually red, square or rectangular box. It may have a button or a small reset lever on it.
If you can't find it in that general area, consulting a 1984 Ford Ranger repair manual or searching online for images of the 1984 Ford Ranger's under-dash area might help you locate it.