Electrical 1988 GT Wrong Cluster- causing electrical issues?

I made a separate thread about an '88 GT that I just brought home last night. Before I went to look at the car the guy selling it said none of the gauges worked besides the speedometer. I get out there, look at the car, and see it has 1990+ 140mph speedometer cluster in it. The car has a good amount of electrical issues such as: the fuel pump comes on when you pull the multi-function switch like you were going to flash your highbeams (even when the key is off), both turn signal indicators on the cluster are always on, the tach doesn't work and randomly jumps around, the headlights don't work (could be bad bulbs, haven't had a chance to look yet), the map light doesn't work, the hvac illumination doesn't work, the cruise doesn't work, I was told the horn is stuck on.

I doubt all of those problems are related to the incorrect cluster being in it but I'm hoping a lot of the problems are related to that. I think I read somewhere the wiring is different between the '87 and '88 clusters compared to the 1990+ clusters.

They also did the classic mod of adding the white overlay.

What typically happens when someone puts an '89+ cluster in an '87 or '88 car?

I doubt they re-pinned it since everything is jacked up. I was planning on pulling the cluster to look on the backside to see what's going on. I was also thinking of pulling the cluster out of my other '88, put it in this car to see if things work again. I am a little worried though because the other '88 cluster is a Motorsport 140mph cluster and I don't want to screw it up if this car has some some of wiring gremlin that would short out or damage my good cluster....

I found the attached diagram for the dash cluster wiring. To make this 1989+ dash cluster work, do I just need to move the location of the wires in the connectors to the postions for the 1990-1993 cluster?

Edit: Is there a good writeup / guide / tutorial of how to make the later cluster work in an 87-88 car? I checked the stickies but didn't find anything there. I did some searching around, found a few threads on the issue but not a good tutorial.