Brett, I have some .jpg files of the wiring schematics for my later rig. But no general schematics.
I have had success using the wire numbering list "from" and "to" to create my own understanding of what the scheme is.
I have no schematic for the chassis relays, but the wire numbers connected to the relays and the wiring number list may yield a clue.
I do have schematics of things like the ignition system, supplement to ignition system for EPM, chassis wiring, battery boost. But I suspect you have similar schematics. They likely do not do what you need.
It does sound like a loose ground wire somewhere that is causing your gauge and lights flickering issue. But I suspect you already made that conclusion.
If you see value in any of the above, I can send copies.
1995 CC Magna #5280
C8.3L 300hp Cummins, 31,000lbs