Illumination Control

I can’t stand Toyota’s logic that if your headlights or DRLs are on that it MUST be night time and therefore the radio dims to night mode. I’d like to install a switch to easily control if the head unit is in Day or Night mode, independent of if my headlights are on/off.
Here is a diagram of my radio’s wiring diagram. I’m assuming “illumination” is the one I’m interested in? Can I simply splice into the constant 12V supply and hook up a switch to this input? (Switch on = 12v, switch of = 0v)

 

No.
The illumination is an input to the radio that "tells" it to dim.
If you want control, place switch to intercept the illumination wire.

 

Thanks. Forgive me for being dense, but please let me know if this is incorrect:

-The orange wire commands the radio to DIM by sending a 12v signal. (0v for bright).
-If I intercept with a switch, the closed position will allow 0v/12v to pass and retain factory dimming logic. Opening the switch will result in 0v and it will always be bright.

I’d like the option of constant day mode and constant night mode. So I would think I’d have to have constant source of 12v to tell it to always dim when the switch is closed, hence why I was thinking of using the yellow wire as a dimming input.

 

Correct. But the illumination wire is not a 0/12v signal. It's a 0v or a pwm modulated signal to indicate brightness level to the equipment.

 

Good to know! Thanks for the info.

 

Incorrect info, Illumination (-) is PWM. Illumination (+) is relay controlled positive. This where you may add the switch.
The drawing you have posted does not indicate an illumination (-).

 

Done! ..almost. The switch isn’t a direct fit so I’ll replace it with one that actually fits. Despite the temporary eye sore of a switch hanging out, it’s totally functional.

Up => dim inhibit => always day mode
Down => auto dim => illumination retains factory logic

https://youtu.be/9Vo9_eg70iU?si=PdQfdQmCcIa9vcHQ