I have not found this written in the documentation, but it seems to be correct based on testing.
The test to perform is simple:
- Perform this test with the key on but the engine not running, and with all other accessories turned off. This will ensure you have a stable test voltage from the battery and the voltage does not fluctuate during testing and that there is no vibration that could be affecting the wires (even if you are sure they are tightly connected).
- Turn on the headlights (or just the park lamps).
- Dim the dashboard lights as low as they go. Observe whether the head unit goes back to full brightness (because the dimming voltage is so low that the unit does not sense it).
- Raise the dashboard lights to full brightness. Observe whether the head unit goes back to dim mode (because the dimming voltage is all the way up). If there is flickering, observe if there is a pattern in how long it takes to switch back and forth.
- Lower the brightness to somewhere in the middle. Observe whether the interval of the flickering changes at different brightness levels.
Some aftermarket radios seem to expect only a 12v on or off on the orange "illumination" trigger wire, but some vehicles (like this Ford van) provide a variable voltage based on the position of the dimmer switch that controls the light level of the dash lights.
It seems the ATOTO F7 (like many other aftermarket units) does not know how to handle a "mid-level" voltage and will blink back and forth between regular and dim modes.
Unfortunately, the only practical way I could find to handle this is to cut the orange wire and not have illumination brightness connected to the headlight switch. (In practice this isn't a problem for my model because there is a brightness button in the status bar on the head unit that you can manually tap to adjust the brightness.) It might be possible to run a wire from the park lamp circuit to handle illumination, but I don't want to risk doing that.