blowing rear brake light bulbs

Hello all

My 850 94 20se estate is starting to get a very large appetite for rear brake light bulbs this includes all three brake lights. I haven’t noticed if one Is blowing more than the other I am just told by the wife that another one as blown. Can anybody help me on this one?.

Mick.

Hi Mick,

It could be a short circuit somewhere along the lines as it seems as though the bulbs are being overloaded - as to where though, I couldn't tell you.

As a starting point check the voltage at the bulb connections with a volt metre.

Regards

Andy

[jaytee]

The usual cause of failed bulbs is age and/or vibration. If its only the rear ones it could be that the previously fitted ones have all gone at about the same time because they have had the same life. The battery voltage should be about the same at all points, and a short circuit would not affect the bulbs, just the fuse or wiring. Are the failed bulbs the same brand, could be from a bad batch. Try fitting a set of branded (Philips/Osram) bulbs and see if they last better. Steer clear of cheep cheep, usually imported from the east, bulbs.

I don't think I have replaced any bulbs in the last 3 years except for one number plate and one rear lamp.

Jim

[170]

My 960 used to do this on one side. The problem was that the bulb holder was knackered so that there wa a resistance on the contact, it got hot when lit and the bulb overheated. The glass was always blackened which is not normal for an old-age failure.

Hello All


I will check the voltage on the bulb holder plus I am not sure of the type of bulb I have used because they came out of the rear lights of a merc van conversion I used to work at coach builders and they had to change the rear lights so the bulbs weren’t any good for some strange reason so you just helped yourself but I have had them for a long time? They are probably the same as me past my sell by date.

Thanks for your help

All the best

Mickintodeep

>The problem was that the
>bulb holder was knackered so that there wa a resistance on the
>contact, it got hot when lit and the bulb overheated.

This is exactly the same problem that I am experiencing on my 1992 850. Thanks for that very helpful piece of advice. I must go to my scrappy this saturday and get myself a new bulb holder.

I had tried all types of bulbs, checked wiring connections etc. Never thought that could happen on a bulb-holder!

Cheers,

Colm
1992 Volvo 850 GLT 20V with 140k on the clock

[ShadeTek]

Measuring the voltage will not do much good as your not putting any load on the socket with your high resistance meter. It will read 12VDC. Either replace the holder or clean the contacts with a fiberglass pen available from TV spares/electronics suppliers and remove the sulphidisation from the contacts. This would then reduce the resistance and hence the heat build up.

[sholtby]

If you are sick of replacing the bulbs buy some LED ones!

Simon

[ShadeTek]

Good idea except every time you hit the brake pedal the bulb failure light will come on........unless you put a dummy load in to take the place of the resistance of the bulb.

[liuleichan]

>Good idea except every time you hit the brake pedal the bulb
>failure light will come on........unless you put a dummy load
>in to take the place of the resistance of the bulb.

Are you sure? Have you checked / tried?

I thought the bulb failure light worked by means of detecting a difference across sides with load on the circuit - rather than a general measuring of the load of each bulb.