Getting sick of this, looking for the manual override to flood the system. Been all over the damn dam, straight ran out of energy ammo. Searching Google for "Vegas" "Eureka" "manual" "override" isn't terribly helpful.

Where the hell is this thing?

Bumpage

Follow the arrows. One should lead you outside the dam, where you knock off a few Legion soldiers and then turn a valve.

Edit: To be clear, I mean the compass arrows.