I was finally able to finish this quest, but it took me about three hours (literally) of fight off untold numbers of waves of arps, re-loading prior saves after running out of potions after fighting off untold numbers of arps, and looking up every walkthrough I could find on the web before I was even sure if I was doing the quest correctly. I thought my game might have been bugged and that the quest just simply wasn't advancing. My game wasn't bugged, I just wasn't doing the quest correctly the whole time because the game didn't make it clear to me what I was supposed to do. I even attempted to force-advance the quest using console commands; the very first time I ever felt like such a thing was necessary, even after having played Morrowind, Oblivion, Nehrim and Skyrim. What was most frustrating was that there is a very simply fix that could have clarified things for me: quest markers. If a quest marker appeared on one of the generators each time we have the chance to attack them in between arp respawnings, then if the quest marker were to switch over to the other generator after the first generator was destroyed, that would have made things so much more clear as to what I was supposed to do.
IF ANYBODY WITH MY PROBLEM FINDS THIS THREAD AND NEEDS TO KNOW HOW TO COMPLETE THIS QUEST:
-I found it helpful to turn off the music so I could hear Jespar/Calia better. They give you commands that can help.
-The generators are those two large, barrel-shaped things that are on each side of the platform that extends out to the switchboards as you face the Black Guardian. They glow blueish-white while there are monsters present but stop glowing when it is your chance to attack them -- in between monster respawnings.
-You can use any weapon to attack the generators; melee, bow or magic.
-The generators can only be damaged when they are not glowing – after the prior wave of monsters has been killed but before the next wave respawns.
HOW TO DO IT: After you kill off the first wave of monsters, you can start attacking one of the generators; it doesn't matter which one you start with. You will then destroy that one generator half-way before another wave of monsters appear. Kill the next wave of monsters. Then go back to THE SAME generator that you have already started working on and this time you should be able completely destroy it. If you don't destroy it this round, keep going back to the same generator until it is destroyed. You will know when a generator is destroyed because flames and smoke will start coming out of the top of it. Once you have destroyed one generator, you do the same thing to the other: Hit the generator and damage it down to 50%, then the monsters will respawn again, kill them, then hit the generator down to 100% and the quest should be completed.