BX19TXD tail light problem - advice needed!

tim · Post by **tim** » Wed Feb 02, 2011 5:27 pm

Before Xmas the wife's BX lost the rh taillight and I couldn't get it back (see posting back down there somewhere). Over that weekend it reappeared between here and Dorset so there was no problem to fix.
It's gone again and this time for good. Here's the problem; I had the usual prod and poke, with bulbs, spare light units etc., but power simply wasn't running through the link loom to the rh side. so I found a live feed by the lh light unit, a brown wire plugged into a green which goes into the bodywork. Here's what I think I've f'd up. I logically said, "live feed to bulb gone. Need live feed NOW. Take feed off brown job and splice into rh tail bulb harness. Lightum up." And yes, that worked fine - the tail light came back. Only prob, the thing went out when you hit the brake lights. Now I've been round in circles here, and frankly the diagrams in the Haynes manual are a struggle to get your head round. MOT time is right now....
As I see it the rh unit is passive, all supply and earths come from the left side. I think it's fine, and changing it doesn't cure the problem. I think my jump from the brown wire doesn't work though I'm not sure why. What does this supply?? The sidelights still work when it's unplugged. I have also run earths direct to the battery (the smaller triple block on the lh unit has two yellow wires which I assume are the major earths; I've clipped a lead to these and the battery. I am well aware that the symptoms might suggest an earth fault but the light goes out completely, not just dims, and the indicator will work fine while all this is going on, as does the reversing light.
Ideas please! My feeling is that the live brown which goes into the green is maybe the start of the problem but where the hell does it go to from there? If it's not that, then what? The green SEEMS to go up the rear pillar and into the roof somewhere but this might be wrong. And how exactly does the output socket in the lh unit receive its 12v supply?

prm · Post by **prm** » Thu Feb 03, 2011 5:53 am

Quite a few possibilities. Upstream faults, bulb faults, n/s to o/s connections on the n/s unit, earths.???
I think??? Your brown wire splice could be the earth return for the number plate lights.??
Disconnect the brown and retry. If this fails?

First I would disconnect both lights. And remove number plate bulbs. Operate all the lights individually; checking with a test meter on the n/s supply multi-pin you’ve got 12v on each circuit plus earths.
Probe all the other pins while testing each circuit to ensure you’ve got no back/cross feeds.
Remove all the bulbs on the n/s and o/s units, Clean and tighten up the contacts on the plugs slightly. Plug in the supply and o/s connectors. Repeat and check o/s multi-pin plug supplies.

Insert the bulbs one at a time for each circuit, apply foot brake, select reverse, and operate indicators left then right.
Hopefully you should be able to identify any circuit faults.. In particular, earth back feeds or loops with indicators and brake lights.

Most probably originally, just a connection with the multi-pin plugs and sockets or faulty bulb holder.

tim · Post by **tim** » Thu Feb 03, 2011 5:30 pm

At last I had an unexpected daylight hour to look at mine. I was wrong about the brown wire from the three-pin block, it is an outgoing feed from the tail light unit, maybe numberplates or owt. So back to the drawing board - shows what happens when you try to fix electrics late at night with a dying torch. Thanks very much indeed for the advice, I will give it another session on Saturday if it isn't pissing down. I am beginning to suspect the input terminal block....

tim · Post by **tim** » Sun Feb 06, 2011 4:41 pm

Still having problems - what a waste of a day! Tried some of the above, no result. Having had a further look at mine, it seems that the first two brown feeds are both live, and the patient had indeed lost one, the second down. I spliced no 1 feed into no.2 thus providing feeds for both terminals. Both tail lights now work lovely (as with previous jump) But the tail light still goes out on the r.h. side when the brake is applied, as does the brake light itself. Aargh. As far as I can tell, all the earths are fine, everything else works all the time in any combination and this problem is confined solely to the brake/tail dept.
What have I missed?? Is there some link between losing the live feed to no 2 terminal and the fact that this is occurring? I can't see how loss of a feed can actually lead to what seems like a dead short. Investigating the fusebox end is doubtless a good thing but actually getting in and out quickly may not be so easy. without removing a lot of plastic.

prm · Post by **prm** » Sun Feb 06, 2011 7:10 pm

Keep at it; some can be a pain in the ass!!
Sorry, forgot to ask. Have you got a tow bar fitted? Any remains electrically, of one being fitted at some time. Also, any signs of a split charging system being installed?
.
Not quite sure with your connections with the live brown splicing???
Would have thought, applying any additional live feeds to the system may cause you additional problems.

A few points to check and try.
Any damage on the ribbon cable running across the boot floor to the o/s unit?
Could be a problem upstream, but if all the individual supply circuits and earths check out with no faults.

Disconnect the multi-pin for the o/s unit and see what happens.
What happens to the number plate lights?
If you’re not loosing, or any lights dim, on the n/s light, would have thought?? The problem lies with the cabling, multi-pins or o/s cluster.

Reconnect the o/s unit.
Remove o/s stop and tail bulbs one at a time and check. Try fitting new or alternative bulbs to stop and tail.
It could be corrosion between the strip connections on the o/s light unit casing or bulb sockets, causing a bridge when the brake is applied.

Clean all the circuit strips and bulb holders on the cluster, scraping any plastic between each strip and bulb contacts. Check for any rust.
Spray all the strips and plastic housing with a coat of acrylic lacquer afterwards.

Best of luck.

tim · Post by **tim** » Mon Feb 07, 2011 10:20 am

A quick check this a.m., what is happening is that when you apply the brakes the power is routed into the tail light filament of the bulb - as the effect isn't reversed, i.e. the tail light is still lighting up the correct filament, not surprisingly the whole lot shuts down. Ideas? Don't forget I have spare light units and changing them doesn't solve it so we can't blame them for some mysterious short. Bypassing the original link loom is the next step but it looks fine, undamaged and so on.

Post by **Defender110** » Mon Feb 07, 2011 1:13 pm

That's the sign of a bad earth.

prm · Post by **prm** » Mon Feb 07, 2011 5:01 pm

I agree with Kevan, with a possible earth fault..

Also, might be worth checking n/s and o/s stop/ tail bulbs and bulb holders.
You might have poor/faulty contacts at the base of a bulb or elements touching.

Any other recent work or bulb replacement on the lighting and electrical systems?

Brian · Post by **Brian** » Mon Feb 07, 2011 5:52 pm

Hi Tim,

Definitely sounds like an earth fault.

This point sometimes fails, worth trying.

Keep at it...

http://www.frenchcarforum.co.uk/forum/v ... highlight=

tim · Post by **tim** » Mon Feb 07, 2011 7:19 pm

Well, like I say, I have some spare light units and have tried those and it made no difference so you can't blame the unit or the contacts which are clean anyway. (I have spent the day doing ball joints and that's the priority for the moment). Don't forget that the RH unit doesn't have a separate earth, the earth runs back through the link loom to the lh unit. All i can do is run a fresh earth from the link loom wire and clip it directly to the battery - this will soon prove the theory! I know it all POINTS to earths, it's simply that every time I've seen earthing problems (usually behind the offending vehicle) you've got taillights indicating, power coming and going etc., and this seems a bit er, focussed. And a live feed certainly left the building at some point. Ah, les electriques francaises.....I just know I'm going to come back tomorrow or the next day and say yes, it was earths all along...... thanks for all the advice so far. More balljoint fun tomorrow if earning an income will allow.

tim · Post by **tim** » Tue Feb 08, 2011 5:26 pm

Problem solved - it looks like the fault was in the earth wire in the link loom where it enters the plug, on the rh cluster. It tested OK on the meter though! I also swapped the cluster backplate for another. Anyway, it's working for now.... thanks for the advice.