Ignition switch question

On a 90 XJ what does the issolated portion that only makes contact on 'start' control? Reason I ask is I'm swapping a 96 steering column into my 90. I have figured all the wiring out with the exception of this and the CC which will be another story all together. I have tried to locate it in my alldata wiring diagrams but couldnt find it (could be missing the correct diagram though)

Thanks

Tim