The id and superego often have a power struggle and this power struggle can easily be seen in the scene where Holly and Harry are on the Ferris wheel.  Harry is identified as the id, the pleasure seeking center.  He strives to be rich and has a greedy complex that causes him to go to extreme lengths to make money.  Harry ends up killing hundreds of people in order to get instant gratification of his desire for money.  Holly on the other hand is seen as the superego because of his sense of right and wrong and his drive to put a stop to the id, or Harry in this case.  Holly's moral values and Harry's greedy desires show a power struggle between both men in this scene.  The both test each other with body movements and gestures.  Harry justifies his crimes with the reward of making money while Holly suppresses his ideals with his moral value, that killing people in order to gain money is wrong.  Both men struggle to over power the other in this scene which can be very similar to id and superego struggle.  The id strives for immediate gratification of their wants while the superego tries to suppress these wants with morals.