He's not offering any quests. Do I have to do something else first?
Sublevels of what building? I already completed all the Empire quests, and seem to be unable to join the Hunters. Is there any other way to befriend the super mutants? How do I sneak past the super mutant guard on the bridge? I am not strong enough to defeat all of them.
How did you find scrapyard? just by wandering the map?
There's a certain quest from one of the peasants in Sedit: Lost City that gives you junk to sell to the guy in scrapyard, perhaps that triggers the side quest.
it is natural You can't get any quests from the hunters if You did all the quests for empire (purge Vault 16 beeig the last one) if You flushed Mutant Huntes from lvl3 of the Vault, than they don't want you in their ranks. those are opposite factions so it's eigther or. Right now Mutant Hunters can only reveal Camp of Mutants on the map ( it's good to talk to Sebastian before leaving to Camp of Mutants. The mutant guard at the entrance must be spoken down. try to Admire his work and then bullshit him You want to tell other mutants/mutant leader how good of a job he does. the dialogue options depend heavily on your speech skill. CoC Robes worn are needed to talk to mutant guard else he'll attack. Save and try a few times. Once inside there's a mutant engineer in a side room. He gives a mini quest to fix power generator (you need electronic parts from scrapyard quest for that the ones after purging Asmodeus Cave). If You fail sneak check by Mutant leader than say who you really are and what do you want from this base. Super mutant leader will give you a quest to lure Mutant Hunter leader Sebastian into a trap. After that go back to Abq. and go talk to Sebastian tell him mutants are gone ad that computer requires his fingerprints to unlock. You'll be teleported to Camp of Mutants and Sebastian will be killed. ( he has the best Big Gun in the game.) after that talk to the leader of super mutants to get a suit of Power Armor. Next go down the elevator to talk to a dying ghoul there. He'll reveal everything.