Installed a new engine panel under the wheel on a friend's Cat 42. Took me two days - someone that knew what they were doing could likely have done it in one. Mark everything, determine function, connect function to function (ignore color code), then try to figure what the extra wire is for?? Lit it all off, no fires, but the engine wouldn't start. Owner finally bailed me out and pushed in the knob for 'engine stop'.
Sounds like you have to do similar. Determine functionality of the new switch - how many positions, what terminals are connected in what positions. You'll have to cut out the old switch - mark both sides of each cut, then determine functionality of the old switch. Connect function to function, then stand by with a 5BC when you light it off.