sometimes if you use the ipod for a long period of time with the headphones plugged in and it is in your pocket the probe for the headhones can bend and crack the insert or the "headphone jack" this is a complex fix but if it is under warranty it should be able to be handled by apple. if not it will cost a pretty penny to replace
circuit boards for the nintendo controllers are very hard to come by. Being that the game cube was not made for excessive online gaming and any competitive play, they will not produce a circuit board. the best option you have is to look at (gamestop, dic replay, play it again sports, & craigslist) to see if they have a new controller for you to purchase
like others were saying its a brake switch at the top of the brake pedal. just did mine and it was a pain but it solved the problem instantly. just need to remove a clip and lift up on the plastic piece to remove it from the brake cable, then disconnect the wiring harness and pop in the new one, atacth the clip and you are good to go.