The headlights won't come on but the main beams work and the sidelights work. The problem isn't the fuses. Oddly the sidelights go off when I turn on the headlights but the sidelights work by themselves and they work when the main beams are on. So I don't think this is a case of both bulbs blowing at the same time (though I haven't checked that yet I must admit). Any ideas?