Because its location isn't standardized, the best approach is to:
1. Consult your owner's manual: This is the most reliable source for the location in your specific vehicle.
2. Look near the fuse box: This is the most common area for its placement.
3. Check online forums: Searching for "1990 Toyota Corolla inertia switch location" on forums dedicated to Toyota Corollas might reveal photos or more specific instructions from other owners.
Keep in mind that some models might not even have an inertia switch. If you can't find it after a thorough search, it's possible your car doesn't have one.