As part of the main quest to find Poseidon within the ruins of las vegas, you will spend a lot of time swimming underwater. The neon-drenched depths are reminiscent of Bioshock but instead of a Big Daddy to contend with, you are dealing with a range of new underwater monsters who want you as a snack.
As part of the Sea of Sands quest, you will be asked to Investigate the Red light but may have some difficulty finding it. Red doesn’t stand out in this brightly colourful underwater cavern, so it does not stick out like a sore thumb.
Where To Find The Red Light
When you try to swim toward the big Lough Ness Monster style machine, the current will be too strong and it blows you back toward the entrance. The way forward is not here. You will need to find another way around. This is where finding the red light is important.
If you load up the game map, navigate to the location marked on the map. This is a lower down area that looks like a ramp into a tunnel. As you swim into this area, look to the left. There will be a sort of balcony overlooking the ramp and on the railing will be a terminal.
If you look close enough, you will see the red light is coming from this terminal. This is what the quest objective is referring to. Interact with this terminal and you will complete the objective and be able to continue on with the quest.