Please can you help?

I've just bought an 8-core 2.66 Mac Pro and two Radeon HD 4870 graphics cards, but each card requires two power cables to connect to the logic board, which has only two connectors. Does anyone know where the two cables to the second card should go? The second card works fine, but I expect the cables are for the cooling fans, so I don't want to fry the second card!