Back lights

[Choosing a name is hard]

The rear wiring harness dropped down and melted on my exhaust . I have pulled the wires apart but now even with the ignition off the back lights are on . Could this be a relay that has burnt out ? Any help appreciated as I don’t have the first clue about electrical things
Pete

 

[Stingray]

Which "back lights"?

 

[Choosing a name is hard]

Hi all
Been away at work
So after a little investigation this is what I found
Front lights work as they should
As soon as battery is connected all break lights come on
4 round ones and the 5 th one in the middle but not the rear side markers
Start car and leave lights off and it is still the same break lights on
Turn the switch to put lights on and break lights go off and 4 back lights come on as well as two rear side markers
Break lights work as they should ( off and on with pedal)
Lights are all led
It has Uk turn signals ( orange in the back lights )and they work as they should
Any help appreciated
Pete

 

[Stingray]

Strange. It's a while since I had a C5 and from recollection C5 is straightforward wiring (as opposed to CANbus introduced for C6) so the problem shouldn't be too hard to find. I don't have an easy answer for you but assuming the melted wiring harness has been correctly separated and insulated I'd try going back conventional bulbs all round and see if that makes any difference. The current draw is different and also by definition an LED bulb ("diode") will only pass current in one direction. A conventional bulb can pass current either way. Conventional bulbs can make fault finding easier when you're using a meter.

I'm trying to remember whether C5 brake lights work with the ignition off. I think they do. This would usually suggest a defective brake light switch but since you say the brake lights can work correctly it seems unlikely. On the other hand your melted rear harness might cause very similar issues if not correctly repaired/insulated.

How did the harness get to melt in the first place? Was some electrical work done at the back of the car? If so I'd double-check all of that. Especially if this is a North American car that's had a light conversion for UK.

Good luck with your search.

 

[Choosing a name is hard]

The harness dropped down onto the exhaust
As said it all works properly except when the lights are turned off even with the ignition off then they light . When they are on ( faulty ) they don’t seem as bright as when the pedal is pressed . This is why I wondered if it could be a relay that burnt out when the initial problem happened

 

[teamzr1]

Not sure if there is any relay as to the brake lights themselves
Lighting wiring is broken up, some goes to the fuse panel in engine bay and some is to the I/P fuse panel in footwell

How many and what colors are the wires that got cooked ?

As stingray mentioned, is this a USA spec or export spec'd C5 ?
Normal stock lighting or some 3rd party type as that plays a part in devices it uses tied into the stock lighting wiring

 

[Choosing a name is hard]

The reason I say break lights is that the 5 th one comes on as well
Once the lights are turned on it goes out and only works when the break pedal is pressed
The car came from Japan

 

[Stingray]

When they are on ( faulty ) they don’t seem as bright as when the pedal is pressed .

That's the classic sign of a problem around dual filament bulbs and quite possibly an earthing problem. The reason for reduced brightness is typically current passing through both filaments of a bulb before making its way to ground. Bear in mind C5 is a plastic car so nothing can ground through the bodywork - there have to be proper earth connections.

A dual filament bulb has three contacts, not four, so the two circuits get connected at the shared terminal. You need to whip those bulbs out and get busy with a decent meter to see what's going on.

Yes, the harness dropped but "why" did it drop? That isn't an everyday occurrence and suggests some previous activity around the back of the car.

 

[Choosing a name is hard]

The lights are LED they have been in there quite awhile now in order to make the lights UK compliant. An extra small piece of wiring had to go in to work the indicators which are now orange the harness that was fastened up badly by me, and dropped down onto the exhaust, as everything works fine now except the lights are on all the time but only the rear ones and I would say it’s the brake light circuit because the fifth light lights when you turn the lights on they work perfectly

 

[teamzr1]

As in my other post, have to know how many wires in that loom and the colors of those that were fried
and also checking the splice pack connections

C5 lighting with stop lights

 

[C5Steve]

I think it's going to need a pic of the wiring to see what's going on, if you're LEDs are like mine there's an additional bit of wiring that connects into the old sockets correct? So the part that melted, is it the old original loom or the new wiring?

Do you have a separate hyperflash harness for the LEDs or does it have resistors built into the new bit of wiring? LEDs only require a very small amount of current so it sounds like whatever has melted has possibly created a short which means the lights are now drawing enough current to stay on. I had a similar when I tried to swap to LED reverse lights, they were on all the time (very very dim).

 

[craigyboy]

faulty brake light switch or it needs to be calibrated

 

[teamzr1]

A faulty brake switch would trip DTCs which OPs is not doing, and brake pedal is not an on/off switch
it is a momentary function

I agree the OP must report as asked multi times how many and what color are the wires that got fried and effects to grounding
which would affect 3rd party lighting systems by back feeding

 

[craigyboy]

A faulty brake switch would trip DTCs which OPs is not doing, and brake pedal is not an on/off switch
it is a momentary function

I agree the OP must report as asked multi times how many and what color are the wires that got fried and effects to grounding
which would affect 3rd party lighting systems by back feeding

That's not the case.. if it needs calibrating it won't show any DTCs and also if broke

 

[Choosing a name is hard]

I will take pics at the weekend as it’s dark in the morning and dark when I get home

 

[teamzr1]

That's not the case.. if it needs calibrating it won't show any DTCs and also if broke

The brake issue did not happen until the wires in the ass end got melted, shorted,
and that does not cause the brake pedal switch to suddenly get out of alignment ?

You really think the controllers are going to allow NO DTCs while the PCM sees the gas pedal engaged, the MPH going up, high RPMs,
higher engine loads, higher MAP readings, torque and brake lights ON non-stop as if that pedal switch was degraded with closed position ?

Suggest you look at the PIDs & DTCs for the EBTCM and the BCM and look at what trips "limp" mode

So in your thinking, the switch can be broken, EBTCM see the wheels speed sensors MPH going down, due to brake on and
just ignore it or the brakes on, but the same controller says MPH is increasing
Limp mode and DTCs were not designed for no reason much less ABS

 

[Choosing a name is hard]

Ok have managed to get some pics and a bit more info
It’s not just the break lights but also the indicators . When I remove the small piece of loom that works the indicators and plug the rear harness into the main harness the back lights still come on when turned off and no key in the ignition . So t think the problem is not in the adapter it’s the main or rear loom ect

 

[Stingray]

Let me say right up front I don't have an answer for you. But sitting and thinking about it there must be significant differences in the wiring between different markets and this inevitably complicates what you are trying to resolve.

On a North American C5 the indicators work by flashing the brake lights. There is just one dual filament lamp in each tail light housing. (In contrast a Euro C5 has two lamps in each housing.) So the indicators on a US car have to flash "on" when the brakes aren't applied and have to flash "off" if the brakes are on and brake lights illuminated. I have never understood how this is achieved but it's obviously done by something at the front of the car, not at the back. Bear in mind also the hazard flasher is in the dash and capable of flashing all the indicators simultaneously. By definition, these two systems have to interact sensibly or the car would have lights going on and off all over the place.

You say your car was originally Japanese market. That will be yet another different wiring set-up because IIRC a Japanese car has no rear fog lamps.

There's a pretty thorough Youtube video here of an American converting a US car to Euro amber indicators etc. From about 11 minutes you'll find him under the dash where he has to cut a white wire - presumably necessary to deal with the "dual purpose" point I mentioned above. So if you've got problems at the back of the car you may need to check under the dash as well.

(OT but note from 14 minutes how easy it is to break off the plastic "bolts" when changing rear side markers. Been there, done that. Araldite is your friend. The "nuts" are intended to cut their own thread in the plastic peg which becomes the "bolt".)

(As regards his need to snap off a bit of plastic from a rear lamp at the end of the video that's only because he's fitted identical lamp housings rather than a reversing lamp housing and an indicator lamp housing. That plastic pin normally prevents the wrong lamp being fitted in the wrong opening. Indicator is usually the outboard lamp and reversing light the inboard lamp.)

 

[Choosing a name is hard]

Thanks for that
It wouldn’t be so bad but all the lights work perfectly once turned on it’s only when turned off even with the key out

 

[teamzr1]

When you say "indicators", you mean the turn signals ?
If so is this effecting all turn signal lights front, rear and left/right ?
How about the backup lights, work OK ?

Are the connectors you show on the right side ?

The 1 wire looking like tape on it is dark green
Review the wiring drawing I posted above and follow that wire that goes to the multi lever of steering column
What is common than is wiring to the emergency flasher

Do not know if non-American models also have the daylight running lights, but is so there are 2 relays in the fuse panel under passenger floor

Use my layout of that fuse panel as to fuses and relays for lighting




Multi levers stalk on steering column, if any contacts got burnt