Hi .
My RR has just failed its MOt as the rear fog lights wont turn off - if the side or head lights are turned on the rear fog lights are on all the time - anyone come across this before ?
It has ungraded xenon headlights and led rear lights ( were all fitted before I bought it )
Everything normally works fine but I cant say I've noticed the fog lights on before but to late now as they wont turn off - if I disconnect the light switch they come on as well ( as do the side lights )
any ideas out there ?
regards and thanks in advance
john

By LED rear lights do you mean the entire cluster or LED bulbs?

If it's a replacement cluster it sounds like faulty wiring as they needed some sort of adapter / relay unit

its the led lights that are the problem....you need specific wiring and modifications to make them work properly..

i would talk to a conversion specialist who can sort it out for you...

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Y. O. L. O.
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A few clues here if you're technically minded

Thanks for the replies - its got complete units fitted not just the led bulbs - while I was having a look my check were - turn the lights on , remove rear lights and check for power at the connectors at the rear lights - power at two points - I'm assuming one is side lights and one is fog lights so I turned everything off and put the indicator/parking light on - now I only have one live at the rear lights - so would this indicate a faulty switch ?

They are not a straight swap - the old units were good old fashioned wiring with 12V & ground for each bulb - the new units have funky 'bus' cabling which sends instructions to the unit - so you need a conversion box of tricks to make them work properly - read the thread I linked & it gives you some idea

If you fit the upgraded 2010/2012 light units on the older cars (like I did) you need to have them configured properly - they are certainly not 'plug n play' Is this where I put the car details and a bit about myself ?........

How long have you had the car ? I assume someone else did the conversion...... you might have to talk to them.

Unfortunately the previous owner did the conversion assured me everything worked ! Yea right - I should have known better - I didn't expect or inspect the rear lights for working ALL the time - more surprised that it passed last years MOT as I bought it with a fresh mot !
but now its off the road till I sort it - currently I'm blinding everyone behind me !

If it had a new MOT when you bought it were the rear lights units changed after the MOT was done? If not then I would go back to the garage who did the previous MOT and query why they passed the car with an obvious fault!

Too late now though its over a year ago - might let off a bit of aggression but it wont get me anywhere - and it still needs sorting correctly !

Are you able to fix wiring yourself?

Hi.
Yea I feel reasonably confident - a diagram always helps .

PaulTyrer wrote:

If it had a new MOT when you bought it were the rear lights units changed after the MOT was done? If not then I would go back to the garage who did the previous MOT and query why they passed the car with an obvious fault!

PaulTyrer wrote:

If it had a new MOT when you bought it were the rear lights units changed after the MOT was done? If not then I would go back to the garage who did the previous MOT and query why they passed the car with an obvious fault!