Synergie brake lights **weird one**

[Firemoth]

Hi. I've been hunting for an answer to this for a few months now (yes it's a bit of a sad one but it's doing my head in! Bear with me )

Firstly, picture the rear lights, the outer ones (not on the tailgate itself), working top to bottom, they're sectioned red, then smoked (or white/clear on the newer ones) and red at the bottom.

When I bought my car in April, the lights were
- brake/tail
- indicator
- nothing

I thought nothing of it till I went to replace an indicator bulb. And found the bottom had a blown 21w bulb. Checked the other side, sure enough that had a blown bulb in the bottom holder too. I replaced the bulbs to see what I got, and I had

- brake/tail
- indicator
- brake

Oo. 4 brake lights. Cool. (because I'm a bit sad like that!)

Moving on a couple weeks, I noticed that my lights had changed again. They were now

- tail
- indicator
- brake

I've checked the top 21/5w bulbs which were fine but I've replaced them anyway, and they're still only doing the tail lights. I can't see any wiring issues, blown fuses or anything. It's like it saves the 21w part of the top bulbs as a backup for the bottom ones. So I've taken one of the bottom bulbs out, nothings changed, it's still only the bottom brake lights (1 now lol).

I can't find any wiring diagrams or anything anywhere to try to explain it. And I refuse to accept a car of this age has a canbus system or anything as advanced as that.

Is there anyone that is sad enough to have contemplated this (like me) and has an answer? It's driving me crackers!

Thanks in advance


This is after putting new bulbs in the bottom (it was the top tail/brake before this, but I don't have a pic of that)

This is a what I noticed a couple weeks later

[Hell Razor5543]

Hi, and to the forum. That does seem a bit strange. I would expect you to have three brake lights (top, left and right), and two fog lights (left and right), all using the higher wattage bulbs. I would be inclined to check all of the bulbs (making sure that the right types of bulbs are fitted in the relevant places, and connected the right way around), and the various connectors to check they are clean, no dirt to get in the way, and the solder joins are all nice and shiny. Other than that I have no further advise (but I feel certain there will be other members who can help).

[myglaren]

Check the earth bonds - a very common cause of problems with rear lights, and as James says, check the bulbs very carefully. Some may appear correct but aren't.
Also the bulb orientation where they have two filaments. Should be difficult to impossible to fit incorrectly but it has happened and with some models causes havoc, admittedly CAN/Van systems but still.

[white exec]

Agree - check out there is a good earths to each lamp position.
Not an uncommon fault on Citroen rear light clusters.

[moizeau]

Just to throw something else into the pot. You have towing electrics. Are these plugged into the rear light cluster or scotch locked? I'd be inclined to disconnect the towing loom and see what happens.

[white exec]

Good thought. Is there also rear-fog switch-out on one of the towing sockets which could be misbehaving?

[xantia_v6]

It is also possible that the BSI detected the previously failed bulbs and went into a backup mode using the rear fog lamps as brake lamps,

You could try removing the lower bulbs and see if the upper ones start functioning as brake lights again.

[GiveMeABreak]

There are no diagrams I have for a vehicle this early unfortunately, but just to confirm bulb types...

Body Wing:
(5) 21/5W LL
(3) P21W

Tailgate:
(4) R5W
(3) P21W

[white exec]

Does the car actually have BSI ? - it's 1997, so pretty early.

[GiveMeABreak]

No - no BSI on the Synergie (1997) Just a fuse box so nothing complicated.

[Doo]

I heard the butler did it

I second the tow bar electrics may be playing up.

I recall early Audi earth faults, watching the car indicate and all manner of disco lights doing their thing

Poor earths can suck power from places you wouldn't even imagine

The higher the wattage required, the more likely the earth fault...

[Firemoth]

Lots of replies! Firstly, no to the bsi. Too early for that. Earth's, I don't believe to be an issue. They're not fog lights, the fogs are the ones on the tailtage itself. If there are any other synergie owners, particularly pre facelift, I'd be interested in pics of brake lights (I know I'm sounding worse )

[white exec]

You might just have to get stuck in with a meter and a test lamp...
If brake lights are out or intermittent, check also the brake light switch (part of the pedal pad?), as these contacts can become burned/dirty/bent.

[Firemoth]

No issue with the brake light switch etc. They're not intermittent, they swapped. I'd be interested to know what other people's synergys are doing with brake lights. Why this bothers me so much, I don't know. But feel free to humour me lol

[van ordinaire]

There seems to be a bit missing the point here, everyone's gone into fault finding mode but, at the moment, we don't know if there's a fault because no one can say what the function of the lowest lamp is.
IF the Synergy has 4 tail lights, the lowest bulbholders should have 5w bulbs in them & if 21w bulbs had been fitted in error they (a) may have burnt out because they're not really meant to burn for extended periods & (b) that overload might not have blown the fuse (as one might've hoped it would) but caused all sorts of other problems. Absent a wiring diagram (& assuming the handbook doesn't help) the colour of the wiring MIGHT help - 'though being a Citroën, probably not