Part in question is the last picture. Needing some help on what this plug goes to. I have it circled. It looks like some kind of solenoid. It is connected to the PCV valve but i dont have a plug anywhere near the area. This is on a 1985 4.9 with a 4spd on the floor. I just recently got the truck from a friend who was using it as a farm truck. Truck did run but extreamly poorly. I have rebuilt the carter yfa and looking to put everything back to factory. Also if anyone have the original air cleaner for this truck in would be happy to buy it. Ill post pics and if y'all see anything else missing or that i need please let me know. Just now getting into this one. I previously had a 84 with a 302 so I'm just now getting back in the game. Thanks for any help

 

Unfortunately, the feedback carb system on the 300 is a somewhat rare beast.
They only made it from 1984 - 1986, and it's very common that most people just yank the whole system out and revert it to the durable/venerable DuraSpark II ignition. That said, you may be hard pressed to find someone who knows what that is.

The system you have was Ford's last ditch effort to keep the carb emissions friendly before finally making the switch to fuel injection. It was a good system that worked well, but as soon as components started to go out, it just tanks in performance and gas mileage due to the computer shutting everything down for safety. (LIMP mode). And due to its rarity, parts are not easy to find.

I really have no idea where that plug goes.

 

Evap canister purge valve

 

that should be near the front of the engine and runs on the vacum line down to the evap canister near the alternator on the frame rail. i just went through all this on my 85 bronco. you will be hard pressed to find any info and anyone who actually knows much about them. if you need photos i can help you out some. im in cali so all this junk has to work on my truch