chocobo
Member Since: 14 Feb 2022
Location: uk
Posts: 35
  
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| Central junction box fault? |
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Hi guys, have an MOT failure with the rear fog light and dash light not working... narrowed down to possibly the central junction box which I know can be an expensive affair! I was wondering if anyone had ever used one of the "send us your CJB and keys and we'll send you a programmed replacement back" type of websites?
Or have any other recommendations because I don't want to shell out £800 on one if I can help it 
Any thoughts appreciated!
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 17th Nov 2022 12:12 pm |
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chocobo
Member Since: 14 Feb 2022
Location: uk
Posts: 35
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Does anyone know if it's possible to just hard wire a new wire and switch mounted on the dash somewhere, directly to the rear fog lights?
I don't know why these things are so over-engineered but to be failing the MOT on something that should be so simple is really frustrating!
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| 18th Nov 2022 12:49 pm |
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Flatlander
Member Since: 20 Jul 2015
Location: Here
Posts: 575
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Yes of course you can do that, it'd be relatively simple to do, even using the existing switch (I assume you've checked the output of the switch?)
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| 18th Nov 2022 1:56 pm |
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chocobo
Member Since: 14 Feb 2022
Location: uk
Posts: 35
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Hey thanks, well the garage checked all wiring and switches and narrowed it down to the CJB, but it is odd nothing else is affected, or is it? I mean that thing if it was dodgy would surely be causing other faults too?
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| 18th Nov 2022 2:30 pm |
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Flatlander
Member Since: 20 Jul 2015
Location: Here
Posts: 575
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Also worth noting that the CJB is essentially just a 'fuseholder' for the rear foglight circuit, you could just bridge the input & output wires with an in-line fuseholder.
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| 18th Nov 2022 2:31 pm |
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Flatlander
Member Since: 20 Jul 2015
Location: Here
Posts: 575
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There is no switching going on in the CJB on the fog light circuits, that's all done by the light switch. There is a 20A fuse in the BJB which supplies power to the fog light circuit, then two individual ones in the CJB which protect both fog light final circuits, the dash indicators are fed from a splice in the wiring harness, it's all very 'old school' TBH, and nothing that should take more than 30 mins to find the defect.
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| 18th Nov 2022 2:35 pm |
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chocobo
Member Since: 14 Feb 2022
Location: uk
Posts: 35
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Hey thanks so much, it's so reassuring to read things might not be as bad or expensive as I was worried! Really appreciate your help will see what I can do wish me luck
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| 18th Nov 2022 2:36 pm |
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chocobo
Member Since: 14 Feb 2022
Location: uk
Posts: 35
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Flatlander wrote:There is no switching going on in the CJB on the fog light circuits, that's all done by the light switch. There is a 20A fuse in the BJB which supplies power to the fog light circuit, then two individual ones in the CJB which protect both fog light final circuits, the dash indicators are fed from a splice in the wiring harness, it's all very 'old school' TBH, and nothing that should take more than 30 mins to find the defect.
Thank you so much! Feeling a lot happier now 
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| 18th Nov 2022 2:37 pm |
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Flatlander
Member Since: 20 Jul 2015
Location: Here
Posts: 575
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TBH, I'd do a bit of poking and prodding yourself, it sounds like the 'garage' are a bit apprehensive of fault-finding....
Check fuse link 2 (20A) in the battery junction box, if OK, then you will get a 12V supply with the ignition on to pin 7 (black-purple 4mm) of the lighting control switch. Set the rear fogs to 'on' with the switch, you should then get 12V at pin 2 of the switch (red-orange 1.5mm) which goes to CJB fuse 32, 15A, the output side goes to the rear fogs & dash indicator.
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| 18th Nov 2022 2:49 pm |
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chocobo
Member Since: 14 Feb 2022
Location: uk
Posts: 35
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Thanks! I'll let you know how it goes, hopefully another success story for this forum 
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| 18th Nov 2022 2:59 pm |
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Flatlander
Member Since: 20 Jul 2015
Location: Here
Posts: 575
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No worries, obviously if any of the checks above fail, then the fault is before that point, if you have the means (a length of wire with an inline fuseholder) you can work backwards by injecting 12V into the circuit, starting at the CJB fuse - with the fuse out, to prove functionality and good electrical connection. Check the fuses with a multimeter or a bulb, sometimes there are hairline fractures that are not easily seen.
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| 18th Nov 2022 3:04 pm |
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chocobo
Member Since: 14 Feb 2022
Location: uk
Posts: 35
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Not been able to test much yet, but did notice the front ones aren't working either (the garage mentioned front ones arent legal requirement but didn't say they weren't actually working either! Does this point to a wider problem with the CJB in your opinion? Either way I suppose as long as I can get the rear one working again I should be able to get it through the MOT
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| 18th Nov 2022 5:22 pm |
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Flatlander
Member Since: 20 Jul 2015
Location: Here
Posts: 575
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No, it points to loss of supply from the BJB or a faulty switch, I'm going to guess at a cause of the front foglight wiring rubbing on the metal bumper and someone 'upgrading' fuse 38 in the CJB to 20A therefore no discrimination between it and the upstream 20A fuse, which has blown and the reason why you have no fog lights at either end.
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| 18th Nov 2022 5:29 pm |
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chocobo
Member Since: 14 Feb 2022
Location: uk
Posts: 35
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OK Thank you, will have a proper look tomorrow then when it's hopefully less cold and dark I had read about the wiring issues on front fogs but also that after 2007 LR had fixed this issue, and as a 2008 thought maybe I'd escaped that, but mostly hoping that's the issue now, thank you again!
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| 18th Nov 2022 5:46 pm |
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Flatlander
Member Since: 20 Jul 2015
Location: Here
Posts: 575
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Like I said, that's just a guess - but if neither front or rear foglights are working, it points to loss of supply to the switch or a faulty switch, whatever the cause.
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| 18th Nov 2022 5:52 pm |
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