* On the frame rail: This is a common location for many vehicles of that era. Look along the frame rails, near the fuel tank. It might be close to the fuel tank straps or near the rear axle.
* In the fuel tank: Some models had the fuel filter integrated *inside* the fuel tank. This is less common but possible. If it's in the tank, you won't see it externally. Replacing this usually requires dropping the tank.
To find it definitively:
1. Consult your owner's manual: This is the best source of information. It will show you a diagram of the fuel system.
2. Check a repair manual: A Haynes or Chilton repair manual for your specific year and engine will have detailed diagrams and instructions.
3. Look at online forums: Search for "1986 Ford F150 fuel filter location [your engine size]" on forums like Ford-trucks.com. Someone may have already posted pictures or descriptions.
4. Visually inspect your fuel lines: Follow the fuel lines from the tank towards the engine. The filter is usually somewhere along that route.
Without knowing your specific engine size (e.g., 302, 351, etc.), it's impossible to give a more precise location. Providing the engine details will significantly improve the accuracy of the answer.
