The fuel filter on a 1988 Ford Bronco II is located
on the frame rail, near the fuel tank. It's usually close to the rear axle, but its exact position might vary slightly depending on engine and options. You'll likely need to get under the vehicle to locate it. It's a cylindrical canister, and often has fuel lines connected to it with clamps.
Because of the potential for slight variations, a visual inspection or consulting a repair manual specific to your Bronco II's engine (2.8L V6 or 2.9L V6 were common) is highly recommended. A picture in a repair manual will be much more helpful than a verbal description.
