Not sure if it's the same for GU's, but I had a weird issue a while back kinda similar to yours. I believe in the GQ, from what I could find/research etc, that there's a common earth that runs into the dash and controls a lot of these.
Mine was frayed in the engine bay and caused me some issues like these, I replaced the bad bit of wire and all good since.
Not sure if it helps, but food for thought.