Hi All,

Thanks in advance for taking a look over my issue here. I'll try to explain it as best I can:

 

RE: Driver's side tail light. 

As far as I can tell the brake light & tail light are the same bulb. 

I noticed that when was car's lights are on the tail light works fine, but when you depress the brake pedal the light goes off. If you are running with car's light NOT on the light does not illuminate at all when depressing the brake pedal.

So I changed the bulb. 

Situation remained unchanged.

So I bought a used tail light (Plastic outer and inner assembly).

I changed these over, fitting a second new bulb. 

Issue remains the same.

Is there something wrong with my wiring? What are my next steps? I really don't want to be failing a future MOT for the sake of a lightbulb...

I've uploaded a video of the issue here:

It starts with the car's lights on, I then ask the wife to depress the brake pedal and you can see the bulb go OFF when the pedal is depressed on the driver's side and flash brightly on the passenger side.

 

The earth (ground, negative) is missing from the rear cluster.

Check the earth wire connection to the chassis earth point near the rear light cluster. Either the wire is broken/corroded or the earth terminal that plugs on to the light cluster is damaged.

The rear tail light which is only 5W is able to illuminate (but not as bright as normal) because it is connecting to ground via the 21W element of the brake light. When you apply the brake a 12V positive supply is sent to the brake light and since now neither the tail light or brake light have an earth both lights fail to illuminate. 

Yep definitely a lack of earth. Happens all the time with dodgy trailer wiring. Reinstate/improve the earth and the problem will go away. 

On 2/4/2024 at 11:09 PM, unofix said:

The earth (ground, negative) is missing from the rear cluster.

Check the earth wire connection to the chassis earth point near the rear light cluster. Either the wire is broken/corroded or the earth terminal that plugs on to the light cluster is damaged.

The rear tail light which is only 5W is able to illuminate (but not as bright as normal) because it is connecting to ground via the 21W element of the brake light. When you apply the brake a 12V positive supply is sent to the brake light and since now neither the tail light or brake light have an earth both lights fail to illuminate. 

 

On 2/4/2024 at 11:40 PM, MJNewton said:

Yep definitely a lack of earth. Happens all the time with dodgy trailer wiring. Reinstate/improve the earth and the problem will go away. 

 

Thanks gents for coming back to me. Total novice here. Do you have any pictures of which the Earth wire is and where it should connect to the chassis? 

 

Thanks. 

 

On 2/7/2024 at 8:45 PM, unofix said:

Follow the RED line on the picture to the connector and it will go to the earth connection on the plug.