There is absolutelly no downside (at least in game) to keep the lowbeams on all all times. Do this, and you'll never have to worry about any headlight offenses. Of course, switch to highbeams when you can't see a damn thing outside, but turn it off when on country roads and with traffic approaching you. #4.
Switch to main (high) beam. There is a dashboard light for main beam which only works if the headlights are on. (I drive an International but I believe this is true for all the trucks.) Wait until nighttime and see if you can see anything in front of you. If you can, your lights are on.
This quick video will help to show how you can turn on the lights for your vehicles in Farming Sim any time it starts to get a little dark. Additionally, we
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