why might both headlights fail simultaneously?

[Norfolkandchance]

My 2007 Mercedes B Class switched its lights on automatically as usual and then immediately displayed an error message that the dipped beam on one side then the dipped beam on the other side weren't working, which they weren't. Main beam and rear lights all fine.

I've had a look for the fuse but the list that tells me which one is which doesn't match-up with the actual fuse box!

Of course it could just be the two bulbs but it seems unlikely. Should I start by replacing them and see what happens?

Thanks

[battered]

Alternator may be overcharging as a result of a reg gone down. Get it checked pronto as otherwise it will boil your battery dry and wreck it. DIY check - start engine, rev to 3000 rpm, battery voltage should not exceed 14.5V and ideally 14.

[VAGslag]

I had an alternator issue which resulted in sudden failure of the alternator and instantly blew both head lights simultaneously... Certainly added a bit of excitement to my night time b-road drive! ha ha!

[kambites]

Could have beewn a voltage surge takin gout both bulbs but equally it could be that one bulb failed which caused a blip which took out the other bulb; I've never seen it happen in a car but it's quite common with domestic lighting circuits.

[paintman]

Simultaneous bulb failure may be unusual but you can't rule it out. Replace & see what happens.
You'll also need to locate whichever fuse deals with the lights as it's possible it could be that.

[Norfolkandchance]

Thanks for all the replies. I replaced both bulbs and they are now working.

[Peanut Gallery]

Thank you for the update!
(Had the same with my brake lights once - both blew very close to each other, close enough for me to think that one blowing caused the other one to go)