The light in the boot of my car does not light up.

I have checked the bulb and it is fine.

I have checked the voltage at the bulb holder without the bulb and with the ignition key turned on and it is 12V

However, when I put the bulb in the holder it does not light up and the voltage is 0, even with the ignition key turned on.

Where is the fault?

Thanks,

Antonio

asalcedo wrote:
The light in the boot of my car does not light up.

I have checked the bulb and it is fine.

I have checked the voltage at the bulb holder without the bulb and
with the ignition key turned on and it is 12V

However, when I put the bulb in the holder it does not light up and
the voltage is 0, even with the ignition key turned on.

Where is the fault?

First thoughts are grounding issues. Is the earth secure? Are both
connections to the battery clean and secure - this should be likely if the
car starts but you never know. Then I think we go into deeper issues
relating to the loom and then difficulties arise. Has the car suffered a
collision and then where? Any wiring connections in that zone?

Good luck.

asalcedo wrote:
The light in the boot of my car does not light up.

I have checked the bulb and it is fine.

I have checked the voltage at the bulb holder without the bulb and with
the ignition key turned on and it is 12V

However, when I put the bulb in the holder it does not light up and the
voltage is 0, even with the ignition key turned on.

Where is the fault?

In our stars?

On Sat, 14 Feb 2009 22:31:41 +0000, asalcedo
wrote:


The light in the boot of my car does not light up.

I have checked the bulb and it is fine.

I have checked the voltage at the bulb holder without the bulb and with
the ignition key turned on and it is 12V

However, when I put the bulb in the holder it does not light up and the
voltage is 0, even with the ignition key turned on.

Where is the fault?

Thanks,

Antonio

Well, clearly that 12V is not across the bulb terminals. If one pin has 12V on
it to earth, then the earth connection to the other pin must be missing. Check
the resistance to earth of the non-12V pin.

In message , asalcedo
wrote

The light in the boot of my car does not light up.

I have checked the bulb and it is fine.


Is there a switch in series with the bulb?

--
Alan
news2006 {at} amac {dot} f2s {dot} com

On Feb 15, 11:31 am, asalcedo wrote:
The light in the boot of my car does not light up.

I have checked the bulb and it is fine.

I have checked the voltage at the bulb holder without the bulb and with
the ignition key turned on and it is 12V

However, when I put the bulb in the holder it does not light up and the
voltage is 0, even with the ignition key turned on.

Where is the fault?

How is the bulb turned on? It's very unlikely to stay on all the time.
I had a similar problem where the bulb was OK and there was voltage to
the connection at the back of the bulb, but no voltage to the contact
that the bulb touched. There was a switch on the wiring diagram but I
could not find it.
I took the bulb holder apart and found a mercury switch inside. The
mercury was coated in oxide. I took the mercury out and cleaned it and
cleaned its container. The switch worked perfectly after that.

Clot wrote on 15/02/2009 :
asalcedo wrote:
The light in the boot of my car does not light up.

I have checked the bulb and it is fine.

I have checked the voltage at the bulb holder without the bulb and
with the ignition key turned on and it is 12V

However, when I put the bulb in the holder it does not light up and
the voltage is 0, even with the ignition key turned on.

Turning the ignition on is not usually necessary to get the boot light
on. There are two places the boot light switch can be fitted in the
circuit - either in the 12v feed to the light, or between light and
ground. Working out which way it is wired and where the switch is, is
the starting point.

If there is 12v at the lamp socket when no lamp is installed, but the
12v disappears when a lamp is fitted - it might indicate there is high
resistance at the boot switch and that the boot switch is wired in the
12v supply to the lamp. There are lots of other possibilities though,
far too many to list.



--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

Matty F wrote :
I took the bulb holder apart and found a mercury switch inside. The
mercury was coated in oxide. I took the mercury out and cleaned it and
cleaned its container. The switch worked perfectly after that.

A mercury switch - that would make it a very long time ago :-)

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

"Clot" wrote in message
news
asalcedo wrote:
The light in the boot of my car does not light up.

I have checked the bulb and it is fine.

I have checked the voltage at the bulb holder without the bulb and
with the ignition key turned on and it is 12V

However, when I put the bulb in the holder it does not light up and
the voltage is 0, even with the ignition key turned on.

Where is the fault?

First thoughts are grounding issues. Is the earth secure? Are both
connections to the battery clean and secure - this should be likely if the
car starts but you never know. Then I think we go into deeper issues
relating to the loom and then difficulties arise. Has the car suffered a
collision and then where? Any wiring connections in that zone?

Good luck.
It sounds like you have a high resistance connection on the +12v wire,
properly at the bulb holder as the boot switch normally switches on the
earth wire.
Trevor Smith

In article ,
Harry Bloomfield writes:
Matty F wrote :
I took the bulb holder apart and found a mercury switch inside. The
mercury was coated in oxide. I took the mercury out and cleaned it and
cleaned its container. The switch worked perfectly after that.

A mercury switch - that would make it a very long time ago :-)

Many years ago, my father had a Citroen GS which had a mercury
switch for the boot light. Being sealed, they are normally very
reliable. Sounds like Matty's one wasn't sealed.

With regards to more recent cars, I've had the both the light
switch fail high resistance due to dirt ingress, and the earthing
of the boot hatch go high resistance through its hinges (which
stopped the rear window heater and rear wiper from working).
In the latter case, I connected an explicit earth tail between
the hatch and the car bodywork, and that was still working fine
when I sold the car ~5 years later.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Mistery solved!

It turns out that there is a switch. Quite hidden under some molded parts. It consists of a metal ball that closes the circuit when the boot door is fully open.

The ball was not making contact with the cable terminals. I replaced the terminals and got the switch working fine.

There was indeed no need to turn the ignition key on. The positive battery pole is always connected to the bulb holder. It is the negative pole the one that is switched by the ball. Thus, there is always 12V between the positive pole at the bulb holder and any metal part in the car, which is connected to the negative pole of the battery.

Andrew Gabriel wrote:

Many years ago, my father had a Citroen GS which had a mercury
switch for the boot light. Being sealed, they are normally very
reliable. Sounds like Matty's one wasn't sealed.

With regards to more recent cars, I've had the both the light
switch fail high resistance due to dirt ingress, and the earthing
of the boot hatch go high resistance through its hinges (which
stopped the rear window heater and rear wiper from working).
In the latter case, I connected an explicit earth tail between
the hatch and the car bodywork, and that was still working fine
when I sold the car ~5 years later.


I'm not sure what Matty saw. Surely mercury would evaporate over enough
time? And I'm really not sure how you clean it. Kind of hard to polish
a liquid!

But only Citroen could put in a boot switch that makes the light come on
whenever you brake...

Andy

On Sun, 15 Feb 2009 20:22:09 +0000, Andy Champ
wrote:

Andrew Gabriel wrote:

Many years ago, my father had a Citroen GS which had a mercury
switch for the boot light. Being sealed, they are normally very
reliable. Sounds like Matty's one wasn't sealed.

With regards to more recent cars, I've had the both the light
switch fail high resistance due to dirt ingress, and the earthing
of the boot hatch go high resistance through its hinges (which
stopped the rear window heater and rear wiper from working).
In the latter case, I connected an explicit earth tail between
the hatch and the car bodywork, and that was still working fine
when I sold the car ~5 years later.


I'm not sure what Matty saw. Surely mercury would evaporate over enough
time? And I'm really not sure how you clean it. Kind of hard to polish
a liquid!

A mercury switch has a curved or bent glass tube with 'contacts'
typically at the middle and one end, and obviously containing a bit of
mercury. As it's tilted the mercury bridges the contacts to complete
the circuit.

--
Frank Erskine

On Feb 16, 12:56 pm, Frank Erskine
wrote:
On Sun, 15 Feb 2009 20:22:09 +0000, Andy Champ
wrote:

I'm not sure what Matty saw. Surely mercury would evaporate over enough
time? And I'm really not sure how you clean it. Kind of hard to polish
a liquid!

A mercury switch has a curved or bent glass tube with 'contacts'
typically at the middle and one end, and obviously containing a bit of
mercury. As it's tilted the mercury bridges the contacts to complete
the circuit.

The mercury switch was in a 1975 Jaguar XJ6. After about 15 years the
mercury was coated in gunk. Fortunately for DIY purposes the switch
was easy to take apart and clean. I think I squeezed the mercury
through a small hole in a piece of cloth and it became shiny again.
The switch was fixed for nothing, and quicker than going for a drive
to a spare parts shop, even if the shop had such a device.

On Sun, 15 Feb 2009 23:56:52 +0000, Frank Erskine
wrote:

On Sun, 15 Feb 2009 20:22:09 +0000, Andy Champ
wrote:

Andrew Gabriel wrote:

Many years ago, my father had a Citroen GS which had a mercury
switch for the boot light. Being sealed, they are normally very
reliable. Sounds like Matty's one wasn't sealed.

With regards to more recent cars, I've had the both the light
switch fail high resistance due to dirt ingress, and the earthing
of the boot hatch go high resistance through its hinges (which
stopped the rear window heater and rear wiper from working).
In the latter case, I connected an explicit earth tail between
the hatch and the car bodywork, and that was still working fine
when I sold the car ~5 years later.


I'm not sure what Matty saw. Surely mercury would evaporate over enough
time? And I'm really not sure how you clean it. Kind of hard to polish
a liquid!

A mercury switch has a curved or bent glass tube with 'contacts'
typically at the middle and one end, and obviously containing a bit of
mercury. As it's tilted the mercury bridges the contacts to complete
the circuit.

The one have in the shed is a straight glass tube with contacts at one
end. The tube has to be tilted to at least 30 deg from horizontal to
let the contacts be bridged. In actual use they were set to flip up to
a vertical position.

Alang wrote:
wrote:
A mercury switch has a curved or bent glass tube with 'contacts'
typically at the middle and one end, and obviously containing a bit of
mercury. As it's tilted the mercury bridges the contacts to complete
the circuit.

The one have in the shed is a straight glass tube with contacts at one
end. The tube has to be tilted to at least 30 deg from horizontal to
let the contacts be bridged. In actual use they were set to flip up to
a vertical position.

I've seen them. What I've never seen is an open one - all the ones I've
seen have been a *sealed* tube.

Andy

On Feb 17, 9:34 am, Andy Champ wrote:
Alang wrote:
wrote:
A mercury switch has a curved or bent glass tube with 'contacts'
typically at the middle and one end, and obviously containing a bit of
mercury. As it's tilted the mercury bridges the contacts to complete
the circuit.

The one have in the shed is a straight glass tube with contacts at one
end. The tube has to be tilted to at least 30 deg from horizontal to
let the contacts be bridged. In actual use they were set to flip up to
a vertical position.

I've seen them. What I've never seen is an open one - all the ones I've
seen have been a *sealed* tube.

The Jaguar mercury switch was not an open one, whatever that is. But
it was easy enough to unscrew to clean it. A pox on sealed *anything*!