98 Vectra problem blowing lights

As above 98 Vectra, about 6 weeks ago i had to replace the passenger side
headlamp and the rear tail light bulbs. They have now blown again (exact
same bulbs) are there any reason why these bulbs should blow and not any
other bulbs?
Simon

 

Had the same problem on my vectra. Only way to get rid of the problem was
to replace all the bulbs in the rear clusters and all the front lights too.

No idea how this solved the problem but it worked!

 

Check the altenator output voltage.
You can do this by measuring the battery voltage while the engine is
doing 3000rpm. Should be no more than 14.5V with the lights on.
If it's above that figure get the battery and alternator checked by a
professional.
Dave

 

Thanks for your replies guys.
I forgot to mention that i had had a new alternator fitted somewhere in
between the the time i origionally replaced the bulbs and now. Can it still
be the same fault with the voltages as its now kicking up the same fault on
2 different alternators?

 

Methinks you should check the earth straps (body to battery, engine to
body/battery) and the earthing arrangments on the front/rear lights.
Dave

 

go with that.
earth straps!
go over the light clusters with a fine tooth comb.

i will guess that it is current related, the bulbs are not blowing through
volts too high, but there is too much current passingthrough them due to an
earthing fault, so they are blowing like fuses.
certainly the way the rear cluster is organised.
not sure on your exact model, but most have a wire which comes off and goes
to the body nearby. this is just a crimp tag & a self-tapper.
that corrodes and causes current flow problems with the eath having to find
another route through another bilb, hence it exceeds it's wattage.

also check the engine/gearbox one.

mike

 

I don't think that can be right. Surely, whatever wiring failure the OP may
have, he'll never get more than 12v (or 14.5v, or whatever the alternator is
chucking out) across any one filament?

 

Yes, the OP has the right idea but for not quite the right reason.
Earthing faults can cause lamps to glow all the time, certain lamps are
not realy 100% rated (21W brake/turn lamps for example) and can
sometimes fail early. Other times they glow dimly
Earth strap faults can cause the altenator voltage to rise, then bulbs
fail. Sometime other expensive stuff (radio, varius ECU's) fails first :=(

Dave

 

who said i was talking about voltage.
i am talking about current.
a bulb is a fuse that glows.
pull too much current through it and it will blow

mike

 

How do you increase the current without increasing the voltage?

My mate Mr Ohm said I = V / R, and I've no reason to doubt him.

 

tis true unless you decrease the resistance. As a filament heats up the
resistance decreases.

Just thought I'd throw my tuppenyworth in!

Mike

 

Shouldnt that read increases? (as the filament heats up)

 

Yes it should. But even so, Ohm's law holds good (for any given R), so the
only possible way for the bulb(s) to carry "too much" current is if they're
defective. Which is where we came in... :-(

 

Ah My friend Mr SodsLaw says Problem with Your theory discounts problem in
circuit,and not bulb. ;o)
--Ikie

 

Just how does Mr Sod reckon I can get >12 (or 14) volts across my likkle
filament. Press the brake pedal extra hard?

 

Honestly If there is a slight short somewhere to the return circuit you get
a mini coil effect
in that area. Causing the current to rise and cook your wires.
We once had a customer who's lights kept blowing on one side only. It turned
out to be
water and a slight crack in the wire causing the current to jump across when
it rained.
--Ikie

 

Humph - you've stumped me. I can understand that you might get spikes, if
there's something inductive in the circuit and you have a dodgy connection
making and breaking. Is that what you mean? But surely in a "steady state"
situation, the max p.d. across any two points (including a filament) won't
exceed the battery (or alternator) voltage? Or am I missing something else?

BTW, I've just crossed Mr Ohm off my xmas card list :-(

 

Yes your right but I find 90% of lighting problems due to either water or
corrosion caused
by water and the said coil effect.
Because the short caused in this way seems to cook whatever is nearest.
The filament or the fuse.
I normally drop the fuse rating in problems like this to save the bulbs
until you find the cause.
I once had a Mini van years ago that caught fire because of the lighting
wires rubbing on the brake lines.
Despite being protected by the fuse!
--Ikie