I'm curious to know if I can simply apply the 12V from the sidelights to an digital pin.
(I'm guessing it can't be done, but am curious about the arduino limits).
When the engine is not running, the battery voltage will be lower than when the engine is running and the alternator is charging the battery. If I can monitor this voltage, I can set a mid-point voltage which the Arduino will switch on the lights when the engine starts, and off when the engine stops.
Isn't that the same as simply detecting the engine running?
The voltage range will be from 12.5V (engine off) to 14V (engine on), so a mid point would be about 13.2V