I don't have the recipe for a foot crank but it seems to me like I should

Ah, the foot crank, my worst nemesis. Useful, yet is a scoundrel, hidden in the dark. It knows I want it, so it leaves without a trail to follow, just for mere spite.

Okay, but more seriously I can’t find the recipe. Out of the skills that seem like they may be relevant, I have Mechanics 3, Devices 2, Fabrication 5. Presumably this would be enough, and in the past, at least, it was auto-learned. Do I now need to find a book or something?

Nothing changed since when your question was answered almost one year ago:

Okay, so they require foot crank, right? How do I get that? Am I misunderstanding something? When I search to install foot pedals it says I need a foot crank.

Foot cranks can be found (garages maybe, sometimes on the street), traded from NPCs or uninstalled from other vehicles (bikes, usually) as long as they are not broken (marked with XX).
They are no longer craftable.