1996 Bonneville SSEI

I have an intermittent issue with the interior lights (front courtesy, lighted front mirrors, rear courtesy, and also the auto dim rear view mirror).

- sometimes the lights and other stuff work as normal
- it seems that after a rain, there is the following issue
- Courtesy lights work when doors are opened or when the headlight switch is rotated to the interior light position
- the sunroof always works
- the foglights always work
- but the foglight switch light is very dim
- the auto dim rear view mirror doesn't work, but the illuminator light on the mirror still is lit
- the individual courtesy lights will not light if you push any of their switches
- if the door is open (lights are on) and you push any of the courtesy light switches, the courtesy light associated with that switch will turn off, and the foglight switch light gets as bright as it normally would
- occasionally, as quick as it starts to act up, it will act normally again

I cleaned all the ground buss bars on each side under the carpet. I also checked the ground wire to the body on the passenger side immediately in front of the passenger door. Battery cables are clean and tight. Generally no other random electrical issues.

My assumption (because of the weird switch operation and the brightening of the foglight switch) that it is some type of grounding issue. Question is where would the ground wire be for the headliner components?

Or can anyone direct me in a different direction to fix this?

Thanks.