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Old 5th August 2020, 09:53   #1
Avulon
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Default Possibly lighting short

Apparently quite a rare fault - I did find an old thread that might be relevant, but thought it better to start anew.


The 1.8t has developed a lighting fault. On turning the lights on the dash illumination will flicker on and immediately back off. The nearside front dip light doesn't work, the offside does. It seems apparent that one side of the lighting circuit is overloading and being cut out by the LSM (correct me if I'm wrong) - Trying the LSM from the other car had the same result so I've ruled that out. I've checked the 50A fuses in the underbonnet and they check out.



My next move was to test all the outputs from the LSM connection plug for short circuits. All the front lights checked out, then I started on the rears. The rear lights have piggy backed towing electrics connected in. And both sides show zero resistance between rear light supply and earth. however both rear lights work.



I started around the car disconnecting bulbs and retesting (expecting to see open circuits). After re-connecting the nearside dip bulb everything started working properly again. ...
... Until used on the road yesterday evening. .



I've already (re)checked both front lamp connections for fraying nearby and had in fact rewrapped the short leads with self amalgamating tape when I did the radiator a couple of weeks ago.



Now looking for other possible causes or theories.
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Old 5th August 2020, 10:59   #2
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The LSM from another car has to be programmed in.---
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Old 5th August 2020, 11:26   #3
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Quote:
Originally Posted by COLVERT View Post
The LSM from another car has to be programmed in.---
Amend to "should" if driven otherwise an "ERR" will probably pop-up. But at rest another LSM will work fine for testing purposes.

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Old 5th August 2020, 11:28   #4
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Quote:
Originally Posted by COLVERT View Post
The LSM from another car has to be programmed in.---

Only if intending to use it permanently .



The spare LSM was only fitted temporarily to see if the issue persisted with an LSM from a fully functioning system. This is perfectly fine. IIRC it's even possible to use the car to drive a short distance before there's any problem with the mileage record, but can't remember how far, so I won't be doing that.
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Old 5th August 2020, 11:52   #5
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Hi Avulon.
have you checked the wiring loom coming from the front OS light which can chaff on the chassis arm bumper off job to check though.
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Old 5th August 2020, 12:07   #6
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I would check the earths in the front footwells. There's two on the driver's side just in front of the door behind the carpet which I believe is where the LSM is earthed, and same on the passenger side. In case anyone's earthed any accessories there and not tightened up the bolts properly.

Strange that the dipped beam worked for a moment after you reconnected the bulb. Have you tried a different bulb? I've had it a couple times with halogen H7 bulbs that would work intermittently due to the bulb being no good.
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Old 5th August 2020, 13:23   #7
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Quote:
Originally Posted by Arctic View Post
Hi Avulon.
have you checked the wiring loom coming from the front OS light which can chaff on the chassis arm bumper off job to check though.

I did inspect them when I did the radiator replacement and also wrapped in self-amalgamating tape at the same time to offer better protection. but I'm prepared to re-examine it.


Quote:
Originally Posted by Rick-sta View Post
I would check the earths in the front footwells. There's two on the driver's side just in front of the door behind the carpet which I believe is where the LSM is earthed, and same on the passenger side. In case anyone's earthed any accessories there and not tightened up the bolts properly.

Strange that the dipped beam worked for a moment after you reconnected the bulb. Have you tried a different bulb? I've had it a couple times with halogen H7 bulbs that would work intermittently due to the bulb being no good.

A bulb change might be on the cards. But when I disconnected the bulb last night and retried the lights the issue was still there.



I'll double check the Earths on the A pillar, thanks for the reminder.
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Old 5th August 2020, 18:00   #8
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And lift the underbonnet fuse box and check for any chafed wires there too.
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Old 6th August 2020, 21:43   #9
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Quote:
Originally Posted by trikey View Post
And lift the underbonnet fuse box and check for any chafed wires there too.
Im think that also, that sharp edge near the fuse box has taken out a few cars.
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Old 10th August 2020, 12:58   #10
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Had another go at it on Sunday, lifted engine fuse box, no sign of fraying that I can see under there. Proceeded to disconnect the rather iffy scotchlock wiring to the nearside rear light for the towbar to rule that out. and,.... ruled out, still an issue. Back to the front - disconnected front nearside h/lamp. things work! reconnect headlight... everything works! spent half an hour and an inch of skin off my wrist wriggling all the wires in the vicinity as well as the wires inside the headlight with an observer/operator in the driving seat. Still working. Drove round the block giving it no consideration over speedbumps and still working. This is annoying. So I have an intermittent fault, somehow related to the front nearside headlight, Possibly influenced by the towbar electrics but can't know that for sure. When will it fail again I wonder. All can do now is use it with lights on during the daytime and keep checking the lights are working properly until it happens or again or confidence is restored.
If it happens again I'll replace the nearside headlamp unit with a spare.
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Need a T4 ?: T4 Owners Map thanks to Stevestrat ( use at your own risk)

Where?:
https://en.wikipedia.org/wiki/Tanelorn
Mods/Retrofits:

PCV vortex 'filter'; bluetooth; inline thermostat; reversing sensors; plenum spyhole ; headlamp washers ; Diy mp3 player replacing CD multichanger; FBH with remote; Headlamp washers; black/chrome front grille, rear blind; Xenon projectors
To do:
puddle lights; 2 Din cd/nav to fit; boot release button
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