help please - Roof light

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SJE

New Member
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7
This is a follow up to my thread regarding an alternator problem. I have a flashing battery lamp which gets brighter with more revs. I also have a rear roof light which has blown. After a lot of expence, the garage has deduced that the alternator needs replacing (plus belt) and the light problem is due to a break in the wiring loom somewhere. There is only 4V at the light. They suggest running a wire from the from headlight to the roof light. When I pointed out that there will still be 8V sinking somewhere with their solution, they agreed. Is it possible that the trailer connector electrics could affect the roof light? I'm currently being fleeced and don't know what to do!
SJE
 
May I suggest that if you are getting 4V at the light - it is unlikely to be a broken wire - It would seem to me that this is more likely due to a high resistance somewhere along the cabling path - most likely poor contacts at a connector somewhere. If you have the wiring spec then follow the cabling through, checking each connector in turn and measure the voltage at each point and clean the contacts at the same time.
To reduce the voltage to 4Volts, something would have to be sinking a huge current and, I think, you would notice the wiring glowing in the dark!
If this is an external roof light - where are you measuring the voltage - it is also possible to have a high resistance earth, which would cause the same effect.
 
Thanks.
I don't have a wiring diagram. Do you know if the 12V supply goes through many connectors on the way to the lamp, and if so, any idea where they are?
SJE
 
I'm also a bit surprised that the bulb doesn't at least glow a little with 4V across it.
SJE
 
I dont if this helps - it might not be for your model, but its betta than nuffink.
 

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Thanks for the circuit diagram. Very useful. I get very suspicious when there are 2 new electrical faults and the garage is not associating them. It seems that the engine has to be revved above 1000 for the battery warning light to go out. Investigation by the garage has shown that there is a back voltage of 1.3V across some resistor behind the dash. Do you know of any relation between the simple light wire dropping 8V and the alternator circuitry gaining 1.3V?
The garage have admitted that they have never seen this back voltage on a Defender, but have seen it on Range Rovers.
I don't like them practicing their electrics at my expence.
Cheers
SJE
 
you could try tracing where the light is plugged into the loom and unpluging in, then see if the alternater behaves itself, then u will know its the light on the roof wiring
 
try calling Paul Edwards on 07768 948055 - he is a sparky specialising in LR vehicles :) he mite be able to help.

He is based in Alton, Hampshire - it might help if yu altered your CP to show whereabouts yu are based :D
 
Had a similar problem on the wifes 110, it was the alternator at fault, this caused the battery light on the dashboard to be illuminated even when the ignition was off. If you have a spare alternator stick it on to see if it solves your problem.
 
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