Depends if u are soldering or using quick disconnects. Either way, you'll probably need some extra wire for the grounds. Solder you need a wire stripper, soldering iron and solder. Disconnects u need a wire stripper, crimper and disconnects.
U just need to connect a different coloured wire from the harness to the NO tab on each of the buttons and the black wire to the tab labelled Common or Ground on each button (wire to one button and then from that button to the next etc).