It's been a long time since i did this, but I'm struggling a bit to see why this couldn't be sorted out with a multimeter and a bit of thought. A normal key-barrel has three basic positions: I) off, II) static-on and iii) momentary-on. The latter is used to fire up the starter - and can fairly-safely be disregarded in this case as that has already been farmed out to a button. If memory serves, then, you should be left with a positive feed - and a bunch of wires that will take that feed (when the barrel is in the static-on position) and light up instruments power the ECU and so on. So, surely, if you can identify the feed from the battery (or FIA switch), the rest will either be redundant (snipped but not removed feeds to the starter solenoid - or push-button switch) or things that want power anyway. i'd start by identifying the main feed. Then try to check if any of the other wires are actually connected to the starter button (they shouldn't be, but measure twice and all that). The feed can go to one side of your new ignition switch - and hopefully everything else that still has a use to the other. By this time, you'll have physically removed the column-lock/ignition barrel from the car and can double-check which connections are common (most of them, probably) before taking a brave pill and flipping your shiny new switch. ...or, at least, that's how I would tackle it if given the problem blind...