Umm… well, I mean, it helps in so far as it explains what the problem is haha.
http://www33.jvckenwood.com/pdfs/B5A-1734-00B_KWV-E_EN.pdf
Thats the PDF instructions for the stereo I have, but the wiring instructions only show “A-6 = Orange/White = Dimmer”. The stereo menus for the dimmer control have three options: ON, OFF, and SYNC, where SYNC is the one that changes the dimmer depending on what the car lights are doing.
Dimmer ON means the screen is bright, Dimmer OFF means the screen is dim… which is weirdly backwards to me as well but its JVC so who knows.
At the moment the screen is going bright when the lights are on, which is obviously backwards.
https://incartec.co.uk/Pages/Product.aspx?P=3264
That’s the wiring adapter I’m using, which as far as I can tell is the same as all the other MX5 adapters (connects2, etc) so I assume they all link to the same wire.
I can’t find the wiring diagram for it though, so I’d have to remove the stereo from the dash to figure out which wire the loom is connecting to - the TNS or the Illumination.
However from your explanation I’m still none the wiser as to whether swapping that wire over will work or not, or end up burning out all the electronics in the car.