I just popped in a new headlight and noticed a “WARNING” on the box telling me to “Always change both headlights at the same time”
I smell BS here but I am hoping some nice electrical type will come along and confirm.
If one headlight goes out, the other is very likely to follow shortly. I’ve always changed both at once just to get it over with.
Oh, but yes, having a warning about it is BS.
After 30+ years of motor vehicle ownership, I call BS. Change one, and the other lasts a week or another year-no way to predict.
on the warning I call BS, but being a little long in the tooth, (the glint in my eye is the sun on my bifocals) I find that if I replace one light and due to better tech it is much brighter than the other one, it messes with my eyes.
I can tell you from sad experience that if you bring the car to the shop and pay me to do just one, I can guarentee that the second one will go bad within a week or two at the most. You will then come back and yell, and make me change the second one for free.
Ask me how I know this.
I always change them in pairs. Had my ass kicked too many times not to.
If you are just replacing the small bulbs of non-sealed beams, you probably bought them in a pack of 2 anyway, so replace both just so you won’t have a loose bulb rattling around just waiting to get broken or lost (save still good bulb for an emergency…if you lose or break it, no biggie). OTOH, if you are replacing those great big honkin’ sealed beam headlights, it’s a wash; do whatever is convenient, but my experience shows that bulb life varies wildly, so there’s no reason to believe that when one bulb goes the other is gonna go any minute.
thanks guys, pretty much what I thought. my work car had 2 bulbs burn out within a couple weeks but my personal car has had one go out twice and the other is still working fine.
As a former employee of the now-defunt Grand Auto chain, I can say with much certainty that the moment you purchase a single bulb, you car knows it.
All kidding aside, if the original bulbs were replaced at the same time, it’s typically a matter of a few days or a week until the other bulb will go out. As far as the warning on the box, I’d write an inflammatory email to the manufacturer. That’s just stupid. They probably tell you not to mix brands, too. Other than common sense telling me that I have two headlights and might as well get two replacements, there’s nothing that would cause the second old bulb to burn out as a result of replacing only one.
lol I read this as “Grand Theft Auto chain”
and they did in fact sort of recomend not mixing brands…not brands so much as types.
I guess that explains why that when I brought my Volvo into the dealer to replace a burned out headlight under warranty, the also replaced the other one, also free of charge.
They said it was a routine move, as the other one often burns out soon thereafter (didn’t provide a reason why and I didn’t ask).
I’ve had my car since new for 12 years, and they did burn out within about a year of each other … not sure if that counts as “together” or not.
Of course, there is always the lazy man’s way. Don’t replace either until both are blown. 
I made sealed beams at Guide for several years, and I never heard of this. Our packages didn’t have that warning.