Strange Dash Lighting Issue - wiring diagrams?

[Pete940]

First off, if anyone has any wiring diagrams for the dashboard/instrument area that would be helpful.

Here's the problem. Many months ago some of the main dash lights started to either go dim or not work at all. Soon after that all the main dial lights stopped working. I still have all the warning lights and the indicator "arrows", just the main dial lights are dead.

I re-soldered (probably not very well) many of the connections on the dash. No change.

I then bought another dash. A single bulb in this dash worked for a moment, then back to nothing again. The bulbs are definitely not blown. The rheostat (the dimmer switch) still controls the remaining instrument lights as normal.

Is it possible that the main dial lights are powered separately from the other dash lights, and therefore maybe this separate wiring system is where my problem lies? Could it just be a bad ground? Where should I look? What troubleshooting can I do?

I'm getting good voltage at the battery.

All suggestions appreciated.