This is where the largest Horde in the game is located. Fortunately, the Checkpoint is at a safe distance from where they sleep so you don’t need to worry about restoring power to the checkpoint. You still need to be careful of the speakers.
The gas can is located to the northeast of the site. You have to bring it over to the inner perimeter of the Checkpoint, where the generator is located as shown below.
For the speakers, there two on each MMU, one in the light pole in the inner perimeter, one in the guard booth at the Checkpoint’s entrance. The last speaker is hidden by trees so head outside the fence to the northwest and you should find it.
Once done, juice up the generator and power it up to restore the power. Loot the NERO Injector from the hard case behind the door to clear this Checkpoint.