In Monquista there are two vendors with ship parts. One has medium hull ship parts and the other has light hull ship parts. I'm trying to purchase parts for my ship light ship hull and the parts should unlock at level 4, my ship is a level 5 now but was a 4 when I was trying to purchase them. All the parts are still locked, am I not understanding this correctly? Is there something else I should be looking for that maybe I still don't have and that is the reason they are still locked?
Do the ship parts match the "Origin" of your ship?
You can't just match up "Light" or "Medium". If you fly a pirate skiff (Light), you cannot use Origin: Monquistador "Light" items on it.
If you mean the two vendors in Puerto Mico in the Tradewinds Skyway (Don't think Monquista City has any ship part vendors?), one has Medium Pirate (Frigate) parts, the other has Light Monquista (Skiff) parts. If you need Light parts for the pirate frigate, I think you need to shop in Gullet (under Jonahtown) in Skull Island, but I might be wrong.
Well, ship part requirements go off of nautical level, I'm not sure if that's what you meant when you said ship level. But, it is worth noting that the second vendor sells parts for Monquistan ships-- look at the origins when you're using a ship, if you have the skull island skiff the Monquistan parts will not fit, since they're for the De Bonzo Galleon (which is, contrary to the name, a skiff). You get this ship either as a crown shop purchase at level eight, or as a quest reward when you're sent to Cool Ranch.
In Monquista, one vendor is for Monquistan ship parts and one vendor is for Pirate ship parts. Monquistan parts cannot be used on Pirate ships and vice versa. Since you don't mention which type of ship you have, I think that you might be trying to put the parts on the wrong type of ship.