Off Road Use Only on fog lights probably has to do with the wattage of bulb being used. Most states have a law about the maximum watts of your bulbs combine that can be used. Something like 200 watts total. So, you take your headlights at 55w and add 50w fog lights, you are going to have 220 watts. Which is illegal, but I would say highly unlikely to get pulled over for.

Oh, and "Off Road Use" means either, our in the boonies, or "track use".

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