S40 tail lights keep blowing
 

Hi, got an odd problem, tail lights keep blowing one by one, tried cheap bulbs, expensive bulbs and genuine bulbs to no avail. Sometimes they last a day, sometimes a month. Holders and plugs free of corrosion, no sign of water ingress, none of the side markers or number plate lights blow. They dont blow in any particular order. What could it be?

Have you physically tested any of the supposedly blown bulbs Tom?

Is it always the same side, is it one at a time or both together or what?

Laird Scooby suggests good checks.

Also, have you had the car long and if so is this problem new or has it happened before?

I ask because a previous owner may have done something 'odd' with the wiring to resolve some issue on the cheap (eg spliced from one side to the other) and you may now be left with that to deal with.

You need to start with a known good situation , buy 4 new bulbs from volvo which are long life ones , measure the voltage at the battery with the engine running , it should not be over about 14.2 volts
The standard bulbs should last several years of daily use . if you use cheap poor quality bulbs you will be forever changing them as there are 4 . they all go at random intervals , you might be changing one or another every month and it gives the false impression that they all go every month . Good job you are noticing it ! Every single neglected old S/V40 I see now has at least 2 bulbs failed at the rear !

What he said ^^^^^^^^

I also see S/V40s with several tail lights out, annoying as blown bulbs are a pet hate of mine!

Replaced all mine with decent ones but also took the time to replace a bulb holder that was knackered.

As above, if still no joy double check someone's not done something odd to the wiring, would be my bet...

That was my line of thought when i queried if the bulbs really had blown.

Something in the back of my mind says some x40s have Valeo alternators, i don't know why but if so, it's worth checking the output as they have a habit of suddenly increasing to about 17-18V for no apparent reason and causing bulbs to blow, strangely on the back more than the front.

Check out Pug/Cit and some Renault models next time you're all out and about to see how many have blown brake and/or tail lights.

At a guess it could be due to standard filament bulbs in the back of the car being a lot less forgiving in voltage spikes than headlights? Useful to know just in case!

Ford Transits seem to eat high level brake lights but not sure if that's just crap bulbs...

The bulbs in the rear end are smaller watage so will have more fragile filaments, that could be a reason as could driving down bumpy roads, especially if the boot is full of stuff.

As for the Transits, the high level brake lights are mounted on the rear doors aren't they? If so, imagine how many times those doors get slammed each day, each slam causing trauma to the filaments...................

how old are your rear shocks crashing though pot holes with failed shocks can play havoc with bulbs. ask me how i know. alternatavly you could try some led bulbs . :regular_smile: