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Discussion summary
YOUR RESEARCHWhy are there no 5 minute jobs with these cars?
Reported or suspected cause
headlight switch or mice love our gen wiring
Reported cause
No successful repair reported for this finding.
1
Identified cause
0
Suspected cause
0
Reported fixes
Read evidence and context
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Discussions that report identifying a cause
1
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Reported cause
the 2 most comon issue is a bad headlight switch or mice love our gen wiring.
Leading evidence: 'headlight switch or mice love our gen wiring' (1 discussions report identifying this cause; no attributable repair resolution). Across 1 matching discussions, the most frequently mentioned possible cause is 'headlight switch or mice love our gen wiring' (1 discussions; 1 report identifying it and 0 suggest it). The most frequently discussed action is 'Check continueity' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Discussions that performed work without a confirmed outcome
1
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Performed · outcome unconfirmed · Original poster
I've swapped the bulbs back to the original and its the same with the original bulbs so I'm pretty sure it's not them.
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Discussions that suspect a cause
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Suspected cause · Original poster
I'm a bit stumped with the right side, I think I need to check the pins to see if anything is getting through to the unit or if the problem is upstream.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that contain suggestions
1
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Suggestion
First thing i would do is check continueity from the tail light to the switch.
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Suggestion · Original poster
The loom on the left side, inside the engine bay is hard to access, I need to take some bits apart but I don't know where it goes to check for a lose connection.
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Suggestion · Original poster
I'm a bit stumped with the right side, I think I need to check the pins to see if anything is getting through to the unit or if the problem is upstream.
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Suggestion
I don�t know if you have other wiring issues going on, but the key to running LED�s on the turn signals is to replace both front and rear and change the flasher relay to a CF-14 version.
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Suggestion
I don�t know if you have other wiring issues going on, but the key to running LED�s on the turn signals is to replace both front and rear and change the flasher relay to a CF-14 version.
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0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion
I don�t know if you have other wiring issues going on, but the key to running LED�s on the turn signals is to replace both front and rear and change the flasher relay to a CF-14 version.
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suspected cause · Original poster
I'm a bit stumped with the right side, I think I need to check the pins to see if anything is getting through to the unit or if the problem is upstream.
Counts describe captured discussions, not unique people or a diagnosis. Author identities are not reliably stored. Exact duplicate evidence is counted once across matching discussions; one discussion counts at most once per action/state. Multiple repairs reported together remain a combination. Suggestions and failed attempts do not establish a fix. Matches cover whole discussions and can include related faults, model variants and incomplete threads.
14 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
Rennlist: 1 discussions
0 evidence records excluded for query context · 0 excluded by outcome qualification · 0 adjusted by outcome qualification.
0 acknowledgements have no verified action link; they do not establish a repair result.
Generation: 20261026T135432Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
2002 C4S, UK based.
I decided to upgrade the light bulbs to LEDs, like I did with a previous classic car. It's a simple job and very satisfying, especially the reversing lights that are so bright you can see where you're going. A nice, simple 5 minute job then.
Or not. The front indicators, repeaters and side lights were indeed simple, especially after I worked out how to remove the headlight units. The rears are where my trouble and strife began.
With 2 bolts each side, removing the units is simple. It's especially simple if on one side, the units have cracked and the bolt holes crumble when you remove then and on the other side not only do they crumble but the aluminium bracket snaps too. Super easy to get out as a result 🤔
After ordering the new bracket plus a pair of Light Savers to bolt the units back in, I now have working lights again. Except I don't.
The first LED bulbs were wrong. The 2nd set had the correct stop/rear lights but the reverse lights don't work any more so I had to switch back to the old bulbs. Then I realised the final issue, the lights don't actually work properly and this is where I need your help.
On the left side, the brake/stop light works but the rear light doesn't. I've checked the bulb and the socket, the fault is actually somewhere further up the loom. The 12v isn't making it down the line to the light unit. This means it's a little dangerous at night. On the right side, the rear light illuminates but the brake/stop light doesn't. Not ideal either. I've swapped the bulbs back to the original and its the same with the original bulbs so I'm pretty sure it's not them. I've checked the fuses, they're all good.
Any suggestions of where to go next? The loom on the left side, inside the engine bay is hard to access, I need to take some bits apart but I don't know where it goes to check for a lose connection. I'm a bit stumped with the right side, I think I need to check the pins to see if anything is getting through to the unit or if the problem is upstream. Help please!
Bloody cars.
02 C4S here in the US.
Boy I feel your pain as I traveled that path 3.5 years ago. In short, I cannot assist - I gave up 😔. I�m running all stock except for LEDs illuminating the license plate.
I�ll be following this, good luck 🤙🏽.
Hhhmmm...five minute job on these cars? Oh yeah...Cleaning the inside of the windshield if you are flexible and fast otherwise none. Back window "fergit about it"!
Lots of possibilities. U have to start at the back and work your way foward.
the 2 most comon issue is a bad headlight switch or mice love our gen wiring.
First thing i would do is check continueity from the tail light to the switch. If none its the wiring, if yes its the switch.
If its the wiring its usually in the engine bay and mice damage. Easiest way to fix it is to pull the harness through to the cabin to make the repair.
Also lately the tail light harness itself has been an issue for some but u said yours was in good shape.
Sounds like u need a decent multimeter and play detective.
I've gone down this path before with similar results. These cars are very finicky when it comes to swapping out standard incandescent bulbs with LED. I found the car didn't like the LED bulbs in certain areas like the brake lights, turn signals, etc. I could swap out the fog lamps and it worked fine. I could swap out the interior dome lights and lower courtesy light on the door and it worked fine. But apparently the car needs to "see" a certain amount of resistance or it thinks there is no light present? You also have to be careful with polarity on LED. I'm sure you found that out.
However, if you're swapping the LED bulbs back with the standard incandescent and it still doesn't illuminate, then you need to put on your detective hat and start investigating the electrical path back to the fuse IMHO. Checking continuity with a multimeter is one method. I've done this MANY times.
For me, it was usually bulb's mount (e.g. like the positive connection was broken or corroded, or the plastic on the fixture was cracked and didn't allow for the bulb to sit properly). I've also experienced problems with the surrounding wires on the light enclosure's harness creating a short or broken off. Again, most of the problems where at the light itself.
The sun shade can be installed in 5 or under minutes as long as you follow the instructions to a T.
As far as the LEDs, I did a conversion a few years ago I only had issue with one of turns. I don't remember what my solution was, I'm guessing I went back incandescent.
I don�t know if you have other wiring issues going on, but the key to running LED�s on the turn signals is to replace both front and rear and change the flasher relay to a CF-14 version. that fixes the hyper-flash. Swapped nearly all my exterior lights 5 years ago and haven�t had a problem since.
Wow, thanks for that info. Hyper-flash
was
my issue. I'll pick up a couple of the CF-14 relays. I really do like the increased brightness with all the distracted drivers these days.
On a side note, if you're not sure of the age of your incandescent bulbs you should check them. My original 23 yo bulbs worked fine but the amber coating was in really bad shape.
Thanks all, it turns out the UK MOT test has expired so I've just given it to the garage to fix!
Regarding Hyperflash, I've bought proper automotive LEDs (classiccarleds.co.uk) that have the right resistance built in and so avoid the issue.
As a wrap up to this, it turns out the bulb holders on both sides were damaged. They were shorting and blew some fuses. I don’t know if I did this when trying to fit the bulbs? Anyway, Porsche only sell the looms, not the holders. Fortunately eBay had a pair for the C4S at less than half the price of new ones. Lesson learnt.
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