The spark plug gap for a 1986 Ford F-150 depends on the engine it has. Ford used several different engines in the F-150 that year. You
must consult your owner's manual or a reliable repair manual specific to your truck's engine to find the correct gap.
Without knowing the specific engine (e.g., 300 inline-6, 302 V8, 351 V8, etc.), it's impossible to give you the correct gap. Using the incorrect gap can lead to misfires and damage to your engine.