While there might be an inertia switch (intended to cut fuel in a collision) it's usually hidden somewhere under the dash or in the engine compartment, and not easily found without a repair manual specific to your year and model. Its location isn't standardized across all 1991 Rangers.
If you need to completely interrupt fuel supply for some reason (e.g., major repairs), you'd likely need to disconnect the fuel pump's power supply at the pump itself (located in the fuel tank) or at the fuel pump relay in the fuse box. This requires some mechanical knowledge and should only be attempted if you're comfortable working on a vehicle. Always disconnect the negative battery terminal first before working on any fuel system components.
