Blowing up the Ammo at the Fortress by Tushhar
Jak II: Renegade on SuperCheats.com
                                       JAK2 RENEGADE WALKTHROUGH: BLOWING UP AMMO AT FORTRESS

Go through the 2 rods. The tank should start shooting at you. Keep on going through until you reach a room with 
platforms spinning. In the middle of the structure supporting these platforms, there should be a blue cylinder 
with electricity inside it. Smash them. There are 2. The easiest way to smash them is to jump on them and press O.
Once you smash both of them, a 'mini video' should come up of 2 rods with electricity flowing between them, turning 
into 2 rods with no electricity going between them. Go through. You should be able to work your way through now.