Inside car lights are dim when you turn on the headlights?

Answer 1

That typically indicates a voltage problem, which could mean a host of issues. the most common is an alternator breeching on failure. this can cause your battery to loose power, and your electronics will behave oddly. ///////if you mean the instrument lighting this is normal you can adjust these with the dimmer mounted somewhere on your dashboard the reason being to preserve your night vision while driving