GCM

I've been gifted a terrific 1989 F150 5.0. Body is pretty amazing (southern truck - no rust) but has some mechanical issues I'm tackling.

I have the Hayes manual in hand but can't identify what this is?

raisin

Fuel vapor canister assembly. Used to limit fuel vapors released to outside air from fuel tank. Full of activated carbon. Vapor line runs from fuel tank to canister to purge valve controlled by computer.
If you wanted it to work you would replace canister, replace any bad hoses.

Pirate Tom

Ditto. Also simply called Charcoal Canister. Like Raisin said, at times when the truck is simply sitting, and not running, when the gas in the tank is evaporating, there are lines running from the top of the tank into that canister. The activated charcoal absorbs the fumes. Then when the truck runs later, it draws the fumes out of the canister, and injects them into your air intake and burns them in the engine, rather than letting the un-burnt hydrocarbons loose in the environment. Entirely not needed for the truck to run, but... real easy to fix if you want, and it's "nice" for the environment. You also don't get that gas smell just hanging around the truck on hot days.

GCM

Thanks so much!