Once you are balancing on his back you are to keep the meter that shows from hitting the edges by using the L3 button (push the left stick in). Eventually you will see the circle symbol appear- when this happens hit the circle button to make him hit a generator. When he hits the one the other will shut down- hit triangle repeatedly while standing on the marker to turn it back on. Connors/ Lizard will charge at you- when this happens swing to the other side and put up the switch. He'll charge at you again, just do the same thing back to the other side. This will bring you back to matching the button presses that appear- the third time he's electrocuted should bring the health bar down to near zero. Wail on him with triangle to finish the battle.