To find it, look closely at the front of the engine block. It's often a heavy-duty cord plugged into a fitting on the engine block itself. It might be somewhat concealed, tucked behind other components or near the radiator. You may need a flashlight to see it clearly.
If you can't locate it visually, consult your owner's manual. It should have a diagram showing the location of the engine block heater. Failing that, a Ford dealership or a trusted mechanic can quickly identify it for you.