Last year the dash gauges and DIC in my 1989 El Dorado flickered a few times and then died. I have been working through parts trying to figure it out, and have hit a wall.

Checked: all fuses and underwood relays.
Replaced: alternator, central power supply, BCM (reused old PROM)

I really don't want to pull the cluster, but I do have an untested spare that came with the car. Outside of that, any good ideas of something I missed that may be causing the issue? I'm really hoping for something stupid simple. Car is running great outside of that. Only has around 78k miles and is sentimental so I don't mind throwing some parts and DIY labor at it.