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Technical Brake Light Not Lamp Or Switch

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Technical Brake Light Not Lamp Or Switch

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jezven

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Nov 24, 2009
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I have a problem with the drivers side brake light not working, It is more than likely my fault as I tapped into it to run the trailor lighting, The display says brake light failure and there is no power to the light I have disconected the trailor wire, I am assuming there is a module that splits the brake light signal and is also the bulb checker, The problem is finding any info on where things are. If anyone can help I would be most greatfull
PS I have run the trailor for 9 years so canot complain to much
Thanks Jez
 
The display says brake light failure and there is no power to the light I have disconnected the trailer wire,

Have you physically checked for power at the wire very close to the brake light cluster? It may be simply a poor connection at the cluster from what you're saying which is quite common. So physically check for power and earth at the cluster and check the bulb as well of course

brake lights circuit.JPG
F30 and F31 are the brake light clusters

I am assuming there is a module that splits the brake light signal and is also the bulb checker
Not really, the body computer does the brake light check and the two rear lights have separate wiring from the BC (2 pairs if you have a MW)
 
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Hi, Thanks Deckchair5, What I have had to do as a bodge is chop the gray wire from the light cluster and run it through a relay from the nearside lamp ,this now gives me both brake lights, Do you happen to know where the unit where the gray wire marked 22 is situated and what its called, Thanks Jez
 
Thanks Deckchair5, I now know I need a body computer M1, When I wired the towbar up I thought it was the same as all my old cars then someone said you should not wire into the cars electrics you should use a relay system, As I had been using the towbar with no problems I left it, still it worked for 8 years, as far as I can gather the unit is in the passenger footwell is this right, Thanks very much for your help
 
Are you absolutely sure there's no power coming out of body computer connector E pin 22?

Putting extra loads on existing wiring through bad installations can easily burn the wiring insulation
 
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I shall check for an output before I buy a new one but at least I now know what to look at and where to check, The only problem you have on these circuits checking for voltage is you have a voltage of about 9v for the test system, mine was reading 11v on the brake circuit but there must be no current, I was even thinking about having a look in the m1 unit as it is likely to be a transister that has burnt out, Jez
 
you'll be needing a '7 way bypass relay'

smart-relay-wiring-diagram2.jpg


basically the trailer lights put too much resistance into the circuit causing a lot of canbus electrics to throw blown bulb warnings and/or shutting down that particular lighting circuit.

The bypass relay takes a feed from your battery and uses a splice from your standard wiring for a 'signal' it then throws feeds down the relvent 'out' wires from the relay module using the 12v feed for its power and not the standard vehicle wiring. if that makes sense then my job here is done
 
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Thanks Richydraper, Thats what I should have fitted when I wired it up, I have just checked I fitted the towbar 9 years ago and have used it a lot. back then light check circuits were quite new.
When I found I should have fitted one, I had been using my tow bar for a while with no problems, And they wanted about £100 for one(before ebay) , I have just looked on ebay they are £15 Thanks Jez
 
I have been at work so work has stopped play, Latest update, I have traced it to the body computer, I changed that with a seconhand one but I have now found out it controls everthing from remote doors, imobiliser, ETC, ETC, so the display just complains because it does not recognise the car or keys, The other thing is how do you thank people, I dont know which button to press and when
 
the little green 'thumbs up' icon under which ever post you would like to thank on the right hand side (next to the quick reply, quote and thumb down icons)

practise with this post ;)
 
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