Yes there is a wire called ILLUMINATION, and generally you want to connect that to your illumination wire in your vehicle. This is a wire that is at 0V when the lights are off and 12V when the lights are on. If you have a "dimmer" wire in there, it might work as well, generally that dimmer wire is a fast pulsed 0v - 12v signal at 100's of times a second or so... it could also be just an adjustable voltage (depending on the age of the car).
Depending on the vehicle you have would be where you can tap off it. Generally cars with modern radios have that wire in the wiring harness to dim the stock radio.
There are 2 different brightness settings, one for day and one for night. I think you can set them to the same brightness. But I doubt that's you problem.
Got to MENU - SETTINGS - HARDWARE - CONNECTION STATUS
And look at the illumination line, does it change with the headlights? If so then you just need to set the brightness (which is set at the factory for very dim) or if it doesn't then you need to hook up that wire.