Hi! The right rear light, bottom bulb doesnt work. The bulb and contact is ok. I cant find fuses for the rear lights? The left rear light, bottom bulb glows weakly, and bright when turning on the fog light. Is the right, rear light, bottom bulb supposed to work the same way?

With the symptom you describe, I'd suspect a faulty earth connection on the light cluster.

Has there been any recent damage or work on that corner?

In Norway do you drive on the right?

In the UK as we drive on the left only the rear right hand FOG bulb illuminates. I suspect it's the opposite in Norway.

The bulb itself should be a duel filament bulb. The other filament is a tail light - 4 tail lights should illuminate (in each light cluster). If the other tail lights illuminate I expect the bulb itself is blown.

1 hour ago, cyberkul said:

Is the right, rear light, bottom bulb supposed to work the same way?

The short answer is no!

Kev.

Edited 7 August, 20257 Aug by tetley
Clarification

2 hours ago, Warrior193 said:

With the symptom you describe, I'd suspect a faulty earth connection on the light cluster.

Has there been any recent damage or work on that corner?

The earth connection is common for all the bulbs in the cluster, and the other bulbs work, so I don't think so. I installed a trailer hook last year, maybe I messed up something.

1 hour ago, tetley said:

In Norway do you drive on the right?

In the UK as we drive on the left only the rear right hand FOG bulb illuminates. I suspect it's the opposite in Norway.

The bulb itself should be a duel filament bulb. The other filament is a tail light - 4 tail lights should illuminate (in each light cluster). If the other tail lights illuminate I expect the bulb itself is blown.

The short answer is no!

Kev.

Ok, maybe you are right. We drive on the right side, and the left foglight illuminates. There is only one center contact for all the bulbs in the cluster, so there can't be any dual filament bulbs. Eg. the top bulb is the stop light, but it acts like a tail light when not pressing the brake pedal. The same with the fog light. The same with the stop light in the right lamp, but in the fog light position there is no light. There is also two separate 3W tail light bulbs outside the clusters on each side.

In the 1z5 version (estate / wagon) the rear lights are electronically driven without fuses.

Lights which only just about shine indicate a poor earth connection (if whole cluster is affected) or poor bulb contact or corrosion if just one bulb affected.

There are no twin filament bulbs in the rear cluster of the estate as they are single filament bulbs electronically controlled. For example the rear light/brake light position has its brightness changed using pulse width modulation to change the brightness. [only the saloon/hatch retains the traditional arrangement].

As said above, in Europe there is only one rear fog light - on the driver's side of the car. It sounds like your weak brightness is the fog light bulb. This can happen if there is poor connection/corrosion in the cluster so another active bulb is supplying power through a high resistance leakage path. Look for water damage.

7 - Twin filament light bulb for the rear fog light and parking light (P21/4W, 12 V, 21/4 W)

According to the workshop manual it is a twin filament bulb. Has somebody put a single filament bulb in the bulb holder? Can that even be done?

Kev.

4 minutes ago, tetley said:

7 - Twin filament light bulb for the rear fog light and parking light (P21/4W, 12 V, 21/4 W)

According to the workshop manual it is a twin filament bulb. Has somebody put a single filament bulb in the bulb holder? Can that even be done?

Kev.

My holder doesn't look like that, I have a wagon. Both are described in the user manual.

8 minutes ago, tetley said:

7 - Twin filament light bulb for the rear fog light and parking light (P21/4W, 12 V, 21/4 W)

According to the workshop manual it is a twin filament bulb. Has somebody put a single filament bulb in the bulb holder? Can that even be done?

Kev.

picture is not good, but there is only one contact in the center of each bulb holder

Bulb 7 is still identified as a dual filament bulb as far as I can see - P21.

I was incorrect in my earlier post. It should be a parking light NOT a tail light.

Forget the above.

It should be the parking light.

30 minutes ago, tetley said:

Forget the above.

It should be the parking light.

There is only one filament in the stop and foglights. Still they are bright or dim, depending on the fog light switch and brake pedal. Some pwm maybe.

9 hours ago, pikpilot said:

In the 1z5 version (estate / wagon) the rear lights are electronically driven without fuses.

Lights which only just about shine indicate a poor earth connection (if whole cluster is affected) or poor bulb contact or corrosion if just one bulb affected.

There are no twin filament bulbs in the rear cluster of the estate as they are single filament bulbs electronically controlled. For example the rear light/brake light position has its brightness changed using pulse width modulation to change the brightness. [only the saloon/hatch retains the traditional arrangement].

As said above, in Europe there is only one rear fog light - on the driver's side of the car. It sounds like your weak brightness is the fog light bulb. This can happen if there is poor connection/corrosion in the cluster so another active bulb is supplying power through a high resistance leakage path. Look for water damage.

I didn't see your answer yesterday, sorry. The weak lights are the same on both rear lights, except that the "foglight position" at right light has no light at all. I don't know if ithey should be brighter. They are clearly visible through the red plastic, and I would say about the same as the two separate 3W tail lights on each side. The ground pin in the contact on the left cluster was burned. Suddenly there were no lights from the left cluster, and the car failed the MOT. The plastic supports around some bulbs also started to brake up. I replaced both clusters from a scrapyard. I'll check today if I messed up myself when I installed a trailer hook. I might have connected the trailer hook electronics to the right "foglight" circuit.

Is your trailer hook up an OE one or a high impedance bypass relay type? Your probably already know but the car monitors the bulbs and if it detects something 'out of specification' it shuts down that circuit. hence, if you have connected trailer wiring direct to the lighting circuit and it is not of the right type the car will perceive a fault and shut down the relevant circuits.

11 hours ago, tetley said:

According to the workshop manual it is a twin filament bulb.

The facelift estate is different and does not look like your picture. Only uses single filament bulbs. Here is the comparison from a driver's manual.

Light unit (Octavia) Bulb

Reversing light P21W

Turn signals PY21W

Twin filament light bulb for the brake lights and tail lights P21/4W

Twin filament bulbs for the rear fog light and rear

parking light P21/4W

Parking lights W3W

Rear light unit (Estate car) Bulb

Reversing lights, brake lights, parking light and rear fog light P21W

Turn signals PY21W

Parking lights W3W

2 hours ago, cyberkul said:

I'll check today if I messed up myself when I installed a trailer hook.

You probably know this, you cannot connect your trailer wiring directly to the car wiring because you must have an interface unit to separate out the sidelight and brake light functions.

The trailer hook has a high impedance interface that doesn't load the original wiring. I had indeed connected the right "foglight" to the interface. The voltage here is rather low due to the PWM control, but I think it still worked when I installed it. I now have connected to the external tail light circuit instead, which has 12V.

The problem was a broken wire, which was caused by a splicing clamp that came with the kit for the trailer hook. I hate those, but I still used it.. Thanks all for your help!

Glad you were able to find the problem and fix it.

Good old crappy scotch blocks strike again 🤣