Welcome to the site! Always great to see the owners of the older model-years coming on board. I'm proud that I offer this welcome line so often - to me it illustrates the durability of these trucks, as our 'generation' trucks are approaching or over 20 years old.
ah, you know those Fords - just won't give up, even when you want 'em to stop :-)
But - all seriousness aside - common problem with our 'generation' is a horseshoe-shaped pot-metal gizmo in the steering column up near the key switch - most good Ford parts counter guys have the part number and bin location memorized - although the typical problem is that the starter will not engage. At any rate, the switch 'rollover' feels different.
This 'gizmo' is what connects the ignition key rotary action to the ignition switch block linear action. The ignition switch block is located down on the steering column near the pedals.
IIRC, one has to pull the steering wheel to get at it.
1989 F150 XLT standard-cab shortbed 4x4, 5.0L, AOD, 3.55 gears, manual hubs, 31x10.50 tires, 215K miles. Repainted Oct09.