To find it, you'll likely need to:
* Look under the dash: Feel around for a small, usually square, box with a button on it. It might be mounted to the frame or attached to a wire harness.
* Check near the fuse box: It's often situated near other electrical components.
* Consult your owner's manual: If you have the original owner's manual, it should have a diagram showing the location of the inertia switch.
* Check online forums: Search online forums dedicated to 1985 Ford F-150s; other owners may have pictures or descriptions of their inertia switch's location.
If you can't find it readily, you might need a flashlight and some patience to thoroughly explore the area under the dash. Remember to disconnect the negative battery terminal before working around electrical components.