Why can't it use the headlight sense?


The player only knows that the line is high or low, and allows you to assign a different dimmer setting to each state, without ever interpreting what that state actually means. The stock kernel doesn't attempt to interpret it.

The button LED code in Hijack assumes that 12V means that the headlights are on, and 0V means that they are off. I'm confident that this will bite us at some point if the button LED hack becomes popular. At some point I'm looking to rework the button LED code anyway - and I'll probably add a Hijack option Dimmer_line_is_inverted or similar. Once that happens then doing stuff like "if (headlights && accessory_line_is_low) {beep}" becomes more feasible.