Is there a diagram anywhere as to the pinout on the actual cluster? I've hacked my car all apart and it might be easier to just splice in some new wires.

 

This might help - click here and find the one you want.

 

All of those are just pages copied directly out of the Chilton. Which is not the most reliable/accurate source for such information.

You should check pages BE-24 & BE-25(pdf pages 1182-1183) in the 88 FSM. And the wiring diagram pages found at the bottom of it(pdf pages 1459-1468).

Right click here, then save target as.

And/or you might also want to take a look at the 88 wiring diagram found here.

Both those sources should have info that applies to 87 as well.