Percius Mercius Ald'ruhn Fighter's Guild Quests
The Ald'ruhn Fighter's Guild quests require you to be the rank of Swordsman (3) and are given to you by Percius Mercius. During the final two quests from Percius Mercius you'll be tasked with killing Eydis Fire-Eye in the Balmora Fighter's Guild as well as Lorbumol gro-Aglakh and Sjoring Hard-Heart in the Vivec Fighter's Guild. It's recommended you tie up any loose ends with these NPCs prior to starting the quests since once you begin the quests they will attack you on sight.
Since Percius Mercius asks you to kill Sjoring Hard-Heart, the leader of the Fighter's Guild in Vvardenfell you'll effectively become the new leader once he's dead. This is an alternative route to becoming the Master of the Fighter's Guild in Morrowind.
Percius Mercius' Quest #1 - The Necromancer of Vas
Other Requirements: Save before going inside // or clear all but Daris Adram before talking with Ulyne so that she doesn't die
For the first quest given to you by Percius Mercius in Ald'ruhn you'll need to take a boat to Dagon Fel and travel west of town to a dungeon by the name of Vas on a small island. Outside the dungeon you'll find Ulyne Henim, an NPC who you'll need to talk to and agree to help clear Vas.
Head inside of Vas and defeat Daris Adram in the Tower portion of Vas. Once this is done Ulyne Henim will thank you and tell you that you're all done here.
Percius Mercius' Quest #2 - Beneran's Bounty
This quest takes place in the same location as the previous one. Return to Dagon Fel via boat then continue west to find the dungeon of Sargon. You'll find our target, Nerer Beneran in the back of the cave - kill him then report back to Percius in Ald'ruhn.
Percius Mercius' Quest #3 - Bandits in Suran
Ride a Silt Strider down to Suran then visit Serjo Avon Oran who is found inside of the Oran Manor on the second floor for a Journal update. After you've spoken with him head northeast to Saturan and clear the entire dungeon of bandits. Report back to Serjo Avon Oran who will give you 1,000G then return to Percius to tell him that you've complete the task.
Tip: Umbra is in this area who will reward you with the Umbra Sword for defeating him.
Percius Mercius' Quest #4 - Flin for Elith-Pal
Our final 'fetch' quest from Percius Mercius requires us to travel to the Elith-Pal Mine which is found northwest of Sadrith Mora (or directly south from Dagon Fel). This dungeon is really out of the way and there really is no good starting point - I typically run from Sadrith Mora (or Jump if my character can cast a high level Jump/Slow Fall spell).
Inside the Elith-Pal Mine you'll want to give the Flin to Dangor whose found in the very back of the mine.
Percius Mercius' Quest #5 - Remove Sjoring's Supporters
Warning: When you accept this quest the next time you come near either of these two NPCs they will attack you. Make sure you've finished all quests you want to do with them first.
For this quest you'll need to visit Balmora and Vivec and kill the other two Fighter's Guild quest givers. This quest puts you on the path to become Guildmaster of the Fighter's Guild but through an alternative means than is typical. Usually you get orders from Sjoring Hard-Heart to kill the Heads of the Thieves Guild then to kill the Master Thief - after which Sjoring will attack you and you'll be made master upon his death.
Percius Mercius' Quest #6 - Kill Hard-Heart
Prior to doing anything with Sjoring Hard-Heart it is recommended that you talk to him about orders and Thieves Guild Bosses. He'll give you a quest along with 5,000G. The only downside to this is you'll be stuck with a permanent Journal entry unless you use a console command.
Unlike the previous two people we had to kill Sjoring will not attack you unless you provoke him. I recommend that you use Frenzy Humanoid or Taunt him enough times until he finally attacks you then kill him. Return to Percius to be named Guildmaster.