Main fuse

The main fuse is a miscellaneous item in the Fallout 3 add-on Broken Steel.

Location
During the quest Who Dares Wins, a broken fuse box is found that activates the train to the left. The main fuse is carried by a robot named presidential metro sentinal unit and it is required to fix the train. Should the robot survive the ghoul attack during the quest, it will eventually replace the fuse box itself.

Related quests

 * Who Dares Wins: Go to the presidential metro and fix the train sitting in the station, then report back to the Brotherhood of Steel.

Bugs
After clearing the area of all ghouls, the (optional) quest of containing the security breach may not trigger as complete, so the presidential sentry bot with the fuse does not complete repairs.
 * To fix, either reload a save or just kill the presidential sentry bot (and loot the main fuse) and do the repairs yourself and then the quest will finish. Having companions wait out of range may also help.