On K bikes the starter button only has power if a) the clutch is pulled in or b) the bike is in neutral. The power to the start button when in neutral is controlled by the gear position circuit board in the instrument cluster. If you swap in another type of instrument cluster or that circuit board goes bad then you'll only be able to start the bike with the clutch pulled in.
However, provided that the gear position switch on the back of the transmission is working properly, you can emulate the functionality that lets you start the bike in neutral with a set of three relays in series.
(http://i278.photobucket.com/albums/kk91/electro_handyman/Bike%20Tech/emaulate_gpi_start.jpg)