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cold



Member Since: 15 Dec 2018
Location: Yorkshire
Posts: 118
Bad earth on rear lights circuit?
Just wondered if anyone has come across this?

1) So when switched on rear lights on at full intensity (brake light level)
2) Therefore press brake - no change but stereo goes blank for 1 second - but no loss of power as doesnt restart and its only the screen - sound is not interrupted
3) Lights off and brake works ok

So at the moment I cant drive at night !

Took some measures off the rear lights

1) Rear lights switched on & no ignition
Voltage at signal to rear lights = 11.96v
Voltage at signal to rear brake = 0v
Voltage between the two signals =11.96v (so rear brake acting as earth?)

2) Rear lights on, ignition on
Voltage at signal to rear lights = 11.34v
Voltage at signal to rear brake = 0v
Voltage between the two signals =11.34v (so again rear brake acting as earth?)

3) Rear lights off, ignition on
Voltage at signal to rear lights = 0v
Voltage at signal to rear brake = 0v
Voltage between the two signals =0v

4) Rear lights on, ignition on , brake on
Voltage at signal to rear lights = 6.76v
Voltage at signal to rear brake = 6.76v
Voltage between the two signals =0v

5) Rear lights off ignition on , brake on
Voltage at signal to rear lights = -4.76v (neg?)
Voltage at signal to rear brake = 6.78v
Voltage between the two signals =-11.55v (neg ?)

Any ideas where to start looking ? only recent change is new
clutch and master cylinder?

Thanks in advance !
Post #844560 18th Jul 2020 4:28pm
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ickle



Member Since: 22 Jul 2010
Location: South Vendee
Posts: 1777
France 2008 Defender 110 Puma 2.4 CSW Alpine White
Main earthing point on bulkhead, somewhere by the master cylinders
Bulkhead to chassis strap by gearbox bell housing
Chek main earth by battery box

Whilst your under and if you've the parts - add some more!

Keith
Post #844565 18th Jul 2020 5:12pm
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cold



Member Since: 15 Dec 2018
Location: Yorkshire
Posts: 118
Thanks Keith - will have a look at them tomorrow, anyone think it might be the brake light switch shorting? worth changing anyway?
Post #844573 18th Jul 2020 5:45pm
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custom90



Member Since: 21 Jan 2010
Location: South West, England.
Posts: 20294
United Kingdom 
You can try adding temporary ground leads too just to see if any change occurs. If it does, you’ll know the culprit to fix right away. ⭐️⭐️God Bless the USA 🇬🇧🇺🇸 ⭐️⭐️
Post #844584 18th Jul 2020 7:16pm
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cold



Member Since: 15 Dec 2018
Location: Yorkshire
Posts: 118
Thanks Steve - if you don't mind how/where could I add a temp earth ?
Post #844593 18th Jul 2020 7:43pm
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ickle



Member Since: 22 Jul 2010
Location: South Vendee
Posts: 1777
France 2008 Defender 110 Puma 2.4 CSW Alpine White
Just run a wire from the -ve battery to tow socket -ve or the bulkhead multi -ve point or into a lamp connector -ve.

As you've been working around the bulkhead - I'd go there first!

Good luck

Keith
Post #844609 18th Jul 2020 8:22pm
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ickle



Member Since: 22 Jul 2010
Location: South Vendee
Posts: 1777
France 2008 Defender 110 Puma 2.4 CSW Alpine White
A~s an after thought, there was a post on here about a faulty tow socket causing all kinds of weirdness!
Post #844610 18th Jul 2020 8:23pm
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cold



Member Since: 15 Dec 2018
Location: Yorkshire
Posts: 118
Thanks Keith!
Post #844620 18th Jul 2020 9:07pm
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custom90



Member Since: 21 Jan 2010
Location: South West, England.
Posts: 20294
United Kingdom 
As mentioned by Keith.

I would remove your transfer box ground stud which is IIRC the RHS of the T box looking towards the front. Clean it and refit.

I had this happen, where it was dirty but not tightened up after a clutch change. All the ground paths were disturbed and I had the whole dash light up like a Christmas tree and external lights if you braked or indicated.

That being said, if you were working in a certain area and the issue developed after that then I’d definitely look there.

Water in the tow socket or plug under wheel arch is possible too.
I fitted an aftermarket tow socket with LED test lights and fully sealed it myself on mine.
The actual culprit was the T box earth though. Have you had any clutch change or t box or similar items removed lately?
Also worth checking the battery posts are tight too.

Good luck. 👍🏻 ⭐️⭐️God Bless the USA 🇬🇧🇺🇸 ⭐️⭐️
Post #844630 18th Jul 2020 9:42pm
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cold



Member Since: 15 Dec 2018
Location: Yorkshire
Posts: 118
Thanks Steve , It wasn't me that changed the clutch so a busy day tomorrow then but thats the joy of a Defender - plenty to learn and do - a hobby first, a car second Thumbs Up
Post #844638 18th Jul 2020 10:32pm
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ickle



Member Since: 22 Jul 2010
Location: South Vendee
Posts: 1777
France 2008 Defender 110 Puma 2.4 CSW Alpine White
scraped knuckles, dirty finger nails and empty wallet syndrome......
Post #844685 19th Jul 2020 8:42am
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cold



Member Since: 15 Dec 2018
Location: Yorkshire
Posts: 118
Or the other woman as my wife refers to it! always unhappy the other woman gets parcels when she doesn’t, she was heard to mutter to the children - and exactly why does it needs brakes Shocked

So, ran earth from -ve to tow bar -ve and ir worked - so I assume faulty earth somewhere Thumbs Up
Cleaned the earthing strap to transmission - no joy
Ran earthing strap from sub earth to tow bar which is grounded on the body - it worked
So logic says -ve battery to chassis is good , its from chassis to rear wiring that is the problem ? So i need to trace that path
Post #844698 19th Jul 2020 10:12am
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ickle



Member Since: 22 Jul 2010
Location: South Vendee
Posts: 1777
France 2008 Defender 110 Puma 2.4 CSW Alpine White
Check multi point on bulkhead - mines LHD so not sure if its in the same place, but not far from main connector to rear loom.....

Good luck

Keith
Post #844700 19th Jul 2020 10:19am
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dorsetsmith



Member Since: 30 Oct 2011
Location: South West
Posts: 4554
chassis loom is grounded on transfer box LH or RH drive
Post #844703 19th Jul 2020 10:52am
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cold



Member Since: 15 Dec 2018
Location: Yorkshire
Posts: 118
So transfer box stud and bulkhead multi stud cleaned and refitted - and still doesnt work - So I assume loom or switch? as an aside is not advisable to wire a new earth even if temporary?
Post #844714 19th Jul 2020 12:00pm
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