Replacing one bulb

congo_90

I'm into motors myself and generally do most servicing/repairs myself so i'm no noob to it all.

Today a friend had to replace a tail light on his car. Simple enough me thinks and send him off to get a bulb. He comes back from halfrauds and fits it. I text him to ask how he got on. He said the bulb packaging recomends replacing two bulbs (one either side) when one blows. I've never heard of this before and seems counter intuitive to bin a working bulb?
Never have I heard of this. Especially as the life of the two new bulbs may blow at the same time now?

Anyone able to confirm if you do this or not? Can't say i've heard anyone ever doing this. Seems halfords were just making an easy sale?

Seth Brundle

I haven't come across that before - either a bulb works and has the right resistance, etc. for the OBC (if fitted) but I don't see any point in treating them like airport runway lights!

colm_mcm

it makes a small amount of sense once you get a car new to replace them in pairs as the bulbs have an expected life, if one goes then there's a good chance the matching one will.

That's the theory.

It also helps sell bulbs

I'd be inclined to replace headlight bulbs in pairs.

Berty

Understandable if they are headlights or more importantly HID bulbs.

biko

Even for headlights I just change the broken one*. I used to change both but then thought "what if I change both and they both go at the same time on a dark road"? Plus, it's faster and cheaper. In my experience it's pretty random when they go.

*unless I swap brand or similar when it'd look odd.

Tropheus

A couple of years ago, one of the tail lights on my Audi blew and I replaced it. Shortly afterwards, the other one would blow and this went on for a couple of weeks with the surviving bulb blowing shortly after the failed one was replaced. I thought I had an electrical problem.

I contacted the dealer and they advised me to change both at the same time. I did that and all is fine. I had the same problem with front side lights.

The only reason I can see is that with one bulb gone, the other gets a slightly higher voltage which blows it. Maybe not, but it makes some sense.

Hal1

Just carry some spare bulbs in the glovebox. If it ain't broken don't fix etc. Simples.

Berty

Hal1 wrote: »

Just carry some spare bulbs in the glovebox. If it ain't broken don't fix etc. Simples.

What? Like a progressive modern country? :eek:

Fishtits

Hal1 wrote: »

Just carry some spare bulbs in the glovebox. If it ain't broken don't fix etc. Simples.

Unfortunately, many modern type motors require a workshop to change a bulb, flog the designers I say...

robtri

I think the idea behind changing bulbs in pairs is good, if you are paying someone/mechanic to change them....
Bulbs have a rated life, so if one goes the liklihood of the the other one going is high...

so it would be cheaper to have the two bulbs replaced at the same time, then in two seperate trips to the mechanics

the same principle is pushed with flourescent bulbs in offices, if one blows replace all of them in the module,

Berty

Unfortunately this is the Motors Tech Help where mostly people will not send you to a mechanic to fix/change something you can do yourself.

Even if the car manual tells you to bring it to a garage you do not have to. It can be done.

A megane for example says bring it to a dealer and my father was confused how to change the bulb. I turned the wheels to full wheel lock and showed his the access for the bulbs in the wheel arch. He was shocked to say the least.

Patience will normally pay off.

Normally the manuals do not like people playing around with HID bulbs because of their connections to ballasts and the like but as long as you don't go smashing around with screwdrivers looking to damage the car/electrics or yourself then you are normally fine.

Heck if a lad in Halfords can do it somebody from Boards.ie can do it.

Tropheus

I've changed Xenon bulbs on my Audi in the past. Took 10 mins max. The owners manual said I'd be struck down by a lighening bolt if I didn't take it to a dealer and pay them €180 for a bulb.

robtri

Berty wrote: »

Unfortunately this is the Motors Tech Help where mostly people will not send you to a mechanic to fix/change something you can do yourself.

but the OP asked not for tech help in installing them, but asked what was the reason for people recommending to change bulbs in pairs...

Yawns

No but Robti said something along the lines of going to a mech to change a bulb

Fishtits

ksimpson wrote: »

I've changed Xenon bulbs on my Audi in the past. Took 10 mins max. The owners manual said I'd be struck down by a lighening bolt if I didn't take it to a dealer and pay them €180 for a bulb.

You are one of the lucky ones, ie you can sort yerself out...

On the other hand, I'd be asking serious questions of the manufacturer if I'd had to replace Xenon type bulbs during the life of the vehicle...

Tropheus

Fishtits wrote: »

You are one of the lucky ones, ie you can sort yerself out...

On the other hand, I'd be asking serious questions of the manufacturer if I'd had to replace Xenon type bulbs during the life of the vehicle...

They only have a life of around 3,000 hours so loose a lot of their luminicity over time. The new ones made a big difference. I used to do a lot of early morning/late evening driving so the bulbs reached their useful life in about 5 years.