A couple of days ago I had a warning of rear bulb failure and it's still there.

After checking, I have some very strange results. Please note I can't find my multimeter so these are purely visual behaviours I saw. All are of the rear - front is ok and not measured.

With lights off:
---------------

• Indicating left --- everything ok
• Indicating right --- everything ok but the right indicator seems to be not as bright as it should be
• Brake --- all brake lights on ok but all other rear bulbs except indicators are very dim, right brake appears not as bright as left
• Reverse --- left reverse ok, right reverse a bit dimmer, both sides fog lights dim

With lights on:
---------------

• Indicating left --- everything ok
• Indicating right --- everything ok except when the indicator is in the on phase - rear tail dims and reverse and fog dim in both sides
• Brake --- both brakes on ok but right appears a bit dimmer than left, reverse and fog in both sides dim - when brake is released all appear ok
• Reverse --- left reverse ok, right reverse dim, both fogs dim, right tail off, left tail dim
• Brake & Reverse --- left reverse ok, left brake ok, left tail a bit dim, right tail off, both fogs a bit dim
• Fog --- left fog ok, left reverse dim, left tail dim, right reverse dim, right fog dim

The behvaiour changes depending whether the main lights are on or off, and problems seem to manifest themselves most on the right cluster but are by no means restricted to it. Also, the dash warning appears mostly only when the brake is applied, and goes away when released.
I initially suspected a ground problem but I would expect this to produce more consistent errors. Grounds in the boot are all secure anyway.
I checked the SLCM. There is no corrosion, joints on the MOSFETs are shiny, no dull or cracked areas in the solder. Same for the multiplugs.
Wiring as far as I can see appears in good condition.
I read some reports that such symptoms could be caused by a dodgy stalk, but I wouldn't expect the range of symptoms I have.
I haven't found my multimeter yet but when I do I will check for grounds, positive, shorts etc.

I suppose there could be some frayed or shorted wiring running the length of the car but there's a lot going wrong and it just doesn't seem to fit that cause.

Can someone point me in the correct direction, based on the results above?
Right now I'm suspecting the SLCM. How can I check that module both in and out of the car? Should I just pay the £30 for a spare (with matching number of course) off eBay? I have no problems replacing components.

Would I be causing problems if I made some jumper wires to temporarily bypass the SLCM lighting circuit completely (leaving the security part of it intact) - is the lighting on a different multiplug than the security? I'd remove the plug and jump between contacts therein.



Thanks

 

It seems like a dodgy earth to me, seems like it is finding its own path to ground via other bulbs/ wiring.

 

When I saw the first fault I thought that too, but different things happen depending on the actions I take, and surely with the same grounding point wouldn't this be an all or nothing thing if there is a dodgy ground?

 

No , because depending on what bulb(s) are lit, determines the path to ground.
It may even be grounding out through the opposite lamp unit.


You may have followed a car at night, all the time it is just the tail lights lit it is OK, then he hits the brakes or indicators and all the bulbs go dim and cycle through a routine including the reversing lamps and rear fogs that were never turned on.


It is just the electrickery trying to ground.

 

Where should I start looking?

 

Renew the bulbs and see if that helps. They are not totally digital and start to burn out.

Also, try electronic cleaner on the bulb contacts to reduce the resistance. On my left rear, a year or so ago, I found the lead that contacts the bulb base was not making good contact: pulled it outward gently, problem has not returned.

Could be a short or broken solder in the multifunction switch -- less likely, fortunately.

 

I haven't got enough spares to renew all of them, but if I swapped the bulbs from each side to the other, would you agree that if it is a bulb probem, symptoms should switch sides too?

 

I had that message once myself, cleared up. I have no bulbs out at all though. The ghosts of Lucas's past, lol

 

Fortunately, there ain't much of Sir John (aka the Prince of Darkness) in the 308s. Pretty much NipponDenso architecture.

Really old RAF jocks still debate whether they lost more mates to the Luftwaffe or Lucas magnetos (for which, I have been told, he was knighted)!

 

I swapped bulbs between clusters but the symptoms remained in their original locations.
Connnections to the bulbs are clean and tight.

Further checking in progress...

 

Next step would be to check the wire loom that runs alongside the starboard boot hinge for a short.

 

It's fixed - I found the multimeter and made light work of it.

My previous ground tests were based on grounds BT20 and BT28R, which are studs in the boot right next to the battery. As I had said before, I had checked these and they were nice and tight and the wiring I could see was good.
Continuity between these and the common ground BT50-2 on the right cluster was... well... wasn't, and I think it measured at something in the MΩ range - very high.
Continuity between ground and common ground BT51-6 on the left cluster was good.
I temporarily connected a wire between BT50-2 and ground - all problems disappeared.

So then I went on to find the break or short. I traced the right cluster ground as far back as I could, but instead of it going to an eyelet on one of the studs (BT28) as the diagram says it should, it went past those and up the side of the fuel tank. From there I don't know because I didn't want to peel back any more sleeve and panels.
I cut it and taped the tail, then pulled back and reterminated to an eyelet and fixed to a ground point.

I think maybe that the diagram I have is wrong, and that the wire I followed from the right cluster actually goes to splice point BTS21, that is instead shown as used by the left cluster and number plate lamps. I'm going to check that at the weekend but for now it's all working ok.

Is this reasonable to suspect the diagram is wrong? I did use the ROW version (09.4) but it's the same for NAS too, so I'm not sure if it's all wrong or just the ROW.

Next job - change the brake pedal switch to hopefully fix failsafe mode problem.

 

Wtf?

 

Erm... I'm not sure if you are doubting my comments or just expressing surprise.

Is there anything I can clarify?