Thank you for your questions and engagement. So I have tried without the heater switches connected and it doesn't affect the lights at all. I have even removed the heater switch illumination wire from the illumination circuit and it doesn't resolve the issue. This leads me to believe permament damage may have been done but I can't say for sure. The heater switches are wired into the 12V power outlets which are a different circuit than the illumination so I would think they can't affect each other.
One big question I have is what the voltage across the switches should be in a normal scenario. There was 11.4V across the fuse which I would expect, but only 2.5-2.6V (.003-.005A) across the illumination terminals at the switches. That makes me think a voltage drop is the culprit. The problem is that I don't have a solid understanding of the circuit because it is so complicated with J/Bs. I can't even say for sure where the various parts of the circuit go to ground. I will repost the circuit as a full file for legibility.
As for the dimmer, I think it's good because it still dims and brightens all the functional lights without issue, and I can see the change in resistance over the A/C illumination wires with my multimeter.
