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UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions.

Car boot light



 
 
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  #1  
Old February 14th 09, 10:31 PM
Senior Member
 
First recorded activity by DIYBanter: Oct 2005
Posts: 345
Default Car boot light

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
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  #2  
Old February 15th 09, 02:21 AM posted to uk.d-i-y
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Posts: 1,369
Default Car boot light

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.


  #3  
Old February 15th 09, 05:53 AM posted to uk.d-i-y
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Posts: 107
Default Car boot light

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?
  #4  
Old February 15th 09, 06:13 AM posted to uk.d-i-y
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Posts: 434
Default Car boot light

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.
  #5  
Old February 15th 09, 07:00 AM posted to uk.d-i-y
external usenet poster
 
Posts: 339
Default Car boot light

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
  #6  
Old February 15th 09, 09:26 AM posted to uk.d-i-y
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Posts: 1,843
Default Car boot light

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.
  #7  
Old February 15th 09, 09:34 AM posted to uk.d-i-y
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Posts: 2,749
Default Car boot light

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


  #8  
Old February 15th 09, 09:36 AM posted to uk.d-i-y
external usenet poster
 
Posts: 2,749
Default Car boot light

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


  #9  
Old February 15th 09, 09:36 AM posted to uk.d-i-y
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Posts: 61
Default Car boot light


"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

  #10  
Old February 15th 09, 09:55 AM posted to uk.d-i-y
external usenet poster
 
Posts: 9,069
Default Car boot light

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]
 




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