Find switch in sewers is a mission in Jak 3. The Freedom League needed the floating KG war factory shut down, but the only way in was to find the cipher glyph to the old Krimzon Guard door systems which were hidden within the main room of the power station. Onin revealed the eco grid inside the main room could help them, but to get inside they would need to find the junction box inside the Haven sewers to de-activate the electric fence at the entrance.
The PlayStation 3 and Vita versions of this mission are related to a trophy named "Switcheroo", completing this mission will reward you with a bronze trophy.
The last mission inside the Haven sewers, you will first meet the new robo-goon unit, which is really a mechanical grunt. As before the Beam Reflexor shines in these close quarter rooms, though the Arc Wielder (with robot shock) is a good choice as well. In the large room up ahead some hover guards attack you, move on and fight through some more robo-goons. After the second laser turret a couple of hopper bots ambush you out of the water, they're very weak however and a Scatter Gun shot or two deals with them just fine.
Several more hover guards and robo-goons attack you up ahead, deal with these until you reach a flooded room with a single spinning laser turret. Get past it to press the button behind it, unlocking a door which reveals a couple more hover guards that attack you. Get rid of them and go into the tunnel to start a cutscene, after which you have to fight a couple sewer frogs.
Time for an obstacle course, you have to make your way up to the other side of this room while fighting against the water which is flowing in your direction. You have to use several constantly moving platforms and pumps to get across the water, while fighting several more robo-goons and some sewer frogs. Due to the water separating you and the robots you might just want to shoot them at a distance.
After this you can walk up the junction box and complete this mission with a cutscene.