Problem with rear lights *Fixed*

[C5Steve]

Bit of a weird one, I've done a lot of searching and can't quite find the issue I'm having.

So, a few days ago when unlocking the car, I noticed the rear marker lights did not come on with the front lights (UK market sidelights, the little spot lights at the front). The reverse lights come on at the rear, but no rear marker or rear running lights. This has become more and more intermittent to the point where now they won't come on more often than not.

Symptoms are:

When unlocking OR turning the lights on, the rear side markers, rear running lights and rear number plate lights don't immediately come on.
They will sometimes come on after a minute or so by themselves, I've seen them flicker slightly at times as well before coming on.
All other lights work as they should, including brake lights, indicators and reverse lights at all times.
The car does have front and rear LED (Radioflyer) lights and LED side markers. These have been installed for years with no issues, all other aspects of the lights are fine except the running lights and side markers.

I know the basics to check, ground points and connectors but it seems very odd it's just the number plate lights, running lights and rear side markers. I would have thought if it was a grounding issue it would be all the lights? Also, the multifunction switch is about two years old or so as I replaced this.

Any pointers on where to start?

 

[teamzr1]

If wiring is stock for C5 I would start at the main ground splice pack 400 I show below

Splice Pack 400 (no ground tab)
Location: taped to rear body harness on right side.
Access requires the removal of the right backup lamp.

Circuits: All rear lamps (tail/stop, turn, marker, license plate, backup, center stop), rear compartment right courtesy lamp.

Check ground splice pack 400 at rear



This has 2 sections that can be pried apart and clean both male and female pins inside

 

[C5Steve]

Thanks JR, I'll have a look at that. The LEDs run off an adaptor harness from the bulb sockets themselves so the harness is stock.

 

[teamzr1]

From the outside of the splice pack would look OK
But as you see, once pried apart may find this :



If that is not the problem than it could be under the trap door under the carpet in the passenger floor facing the firewall

There is where the BCM controller, fuse panel and car's network is
Closely look for any wiring issues, water or animals eating wiring

The BCM is in part what controls the lighting

 

[C5Steve]

From the outside of the splice pack would look OK
But as you see, once pried apart may find this :

View attachment 26463View attachment 26464View attachment 26465

If that is not the problem than it could be under the trap door under the carpet in the passenger floor facing the firewall

There is where the BCM controller, fuse panel and car's network is
Closely look for any wiring issues, water or animals eating wiring

The BCM is in part what controls the lighting

So, having just been under the car it appears to be the splice pack. Moving it about caused the lights to go on and off, upon opening it I can see it's corroded as well so I'll clean it up. Just need to find my contact cleaner which I know I bought in November (thanks Amazon) but has magically vanished now I need it!

JR do you know if the rear connectors come apart? The pics above are of the front ones I'm pretty sure.

 

[teamzr1]

Glad that was help in debugging the problem

As my images above
Splice packs are 2 sections, the top as you see are male pins
The bottom half which the wires go in have female pins

Problem is, there could be so much corrosion that you cannot pry them apart
Most people cut the pack off and simply splice all the ground wires together and make sure you waterproof to prevent trouble in future

 

[C5Steve]

Yeah thanks JR, to be clear it wasn't the ground splice pack that was the issue it was the connector for the rear loom. There's just one ground wire on the passenger side off the loom to the stud in the frame rail. That was fine, it was the pins in the plug. See highlighted connector below:



The connector wasn't too bad, just a couple of pins that were a bit grubby. No where near as bad as the pics you posted anyway. I've cleaned them up for now and tucked them out of the way, I'll look at taking them apart in the next few days and getting inside them.

 

[teamzr1]

OK, I see which connector


Need some contact cleaner, or MAF cleaner or electronics cleaner

 

[C5Steve]

Yep, found my contact cleaner in the garage and gave it a good scrub both the male and female sides. Thanks again!