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k11pol
Monza


Joined: 18 Feb 2010
Posts: 151
Location: Aberdeen


PostPosted: Wed Nov 11, 2015 9:07 pm    Post subject: Rear light failure Reply with quote

I have after market LED s fitted to the rear of my 997.1 and have just had the warning light come on telling me there's a fault. When I checked it the light only comes on when I press the brake not when purely just switched to on.

Would this point to an electrical fault or a fault with the light cluster itself and if the light can the LEDs be fixed or would I have to replace the whole unit ?
 
  
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GT4
Nordschleife
Nordschleife


Joined: 08 Nov 2008
Posts: 30192
Location: Hertfordshire and Hampshire


PostPosted: Wed Nov 11, 2015 9:24 pm    Post subject: Reply with quote

When you say "fitted", did the fitter not test them?

Not much to go on, but I'd be inclined just to return/replace to rule out lamp failure.

If I were in a fiddling mood, I'd add a resistor (or in relative terms, a shunt, in parallel) to the high level brand light (at least temporally to test).

If that sorted it, too high a resistance would be the indicative failure mode.

Therefore leave a suitably tidy (and long term wattage) resistor in there.
 
  
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k11pol
Monza


Joined: 18 Feb 2010
Posts: 151
Location: Aberdeen


PostPosted: Wed Nov 11, 2015 9:38 pm    Post subject: Reply with quote

The lights were bought and fitted 4 years ago. I bought them from a member on here and fitted them myself as it was straight forward plug n play. As for fitting a resistor , I wouldn't know where to start.
 
  
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GT4
Nordschleife
Nordschleife


Joined: 08 Nov 2008
Posts: 30192
Location: Hertfordshire and Hampshire


PostPosted: Wed Nov 11, 2015 10:06 pm    Post subject: Reply with quote

Your opening sentance sounded a bit passive/third-person, so it implied you weren't involved.

Apologies for the incorrect inference.

If you can't return them and a resistor fix is beyond you, I'd suggest someone else take a look (not being funny, but the resistor test is just - almost - literally tying a resistor across any pair of brake wires, ie +/-, the perfect test resistance is in fact a spare brake bulb!)
 
  
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k11pol
Monza


Joined: 18 Feb 2010
Posts: 151
Location: Aberdeen


PostPosted: Thu Nov 12, 2015 2:33 pm    Post subject: Reply with quote

I'm going to swap the lights over just as a test and that should tell me if it's an electrical fault or the led unit that's faulty. Don't have time today though so probably do it over the weekend.
 
  
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k11pol
Monza


Joined: 18 Feb 2010
Posts: 151
Location: Aberdeen


PostPosted: Fri Nov 13, 2015 1:12 pm    Post subject: Reply with quote

Ok, I swapped the lights over this morning and the fault moves from right side to left side so it is the LED unit itself that's at fault unfortunately. Looks like I'll be ***** out another £400 . With the lights swapped round and the fault on the left it still shows on the dash that the fault is on the right side , any idea why this is as I would have thought that it would have said left side ?
 
  
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Clanky
Imola


Joined: 24 Aug 2012
Posts: 855
Location: Scotland

2007 Porsche 997 Turbo

PostPosted: Sun Nov 15, 2015 5:39 pm    Post subject: Reply with quote

k11pol wrote:
Ok, I swapped the lights over this morning and the fault moves from right side to left side so it is the LED unit itself that's at fault unfortunately. Looks like I'll be ***** out another £400 . With the lights swapped round and the fault on the left it still shows on the dash that the fault is on the right side , any idea why this is as I would have thought that it would have said left side ?

Maybe worth swapping back both originals to see if that cures the fault & take it from there.

Check & clean all of the connectors again.

If they are aftermarket LED units, they should have built in resistors to fool the CANBUS into thinking there is a bulb there. It could be that the resistor has failed. Without seeing inside the units, it's hard to judge how they are made, but the other possibility is each LED has its own resistor which sounds unlikely if the whole unit is out. It does sound as if there may be an electrical issue if the fault has moved to the other side of the car.
Can you tell from the other unit if the LEDs are functioning as stop / tail lights (dual brightness) or separate LEDs for stop & tail? If they are different LEDs then maybe just one circuit has failed due to a dry solder joint or bad connection.
_________________
996 C4s (Gone)
997 Turbo

S3 Daily Driver
 
  
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k11pol
Monza


Joined: 18 Feb 2010
Posts: 151
Location: Aberdeen


PostPosted: Tue Nov 17, 2015 7:17 pm    Post subject: Reply with quote

I ordered a new set of Dectanes on Friday so will just try fitting them once they arrive. When I get time I will look at or get someone else to check out the LEDs that are not working as it could be an easy fix for someone in the know.
 
  
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