At least the column harness, I don't recall if there were more changes beyond that. There definitely are if you want to use the 89+ gauge cluster's cruise indicator and you may need to delete the pre89's primary control switch... you'll be needing a 89+ column too.
Just look at the wiring diagrams, there are plenty of links to them here, Cygnusx1's if for a '90 or '91. The pre89 you'll need to download in PDF format. I think the turboninja website is still a good source.
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