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Braking Causes All Lights To Flash On, Or Brake Lights Constantly On


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I have a 2005 reg Fiesta 1.4 Zetec, owned for about 4 months.

I recently had a brake light out, so using the Halfords online part finder using reg number I reserved and collected some bulbs, being naive about this kind of thing I assumed they would have got it right.

When I changed both brake lights I noticed that whenever I braked that the headlights, cd player light and light behind the speedometer etc all lit up whenever the brake pedal was pressed.

The only way for this not to be a problem when driving (don't want to be flashing the person in front every time I brake) I thought it best to turn the headlights on. However I then noticed that instead of the tail light being on it was the full brake light that was on.

I went to Halfords on the way home to check that I had the right bulbs, they said I had not and they gave me the correct ones for free.

I have swapped these over now I still have these problems.

-If the bulb is in place in right and left then whenever I brake all the lights flash as mentioned above

-If the bulb is in place in right and left then whenever the headlights/taillights are turned on the brake lights are lit up constantly so people cannot see when I am actually braking

-If the right hand brake light bulb is taken out then the left & middle brake lights work as normal, no flashing of all the other lights

-If the right hand brake bulb is taken out then when the headlights are turned on I get no tail lights at all, but the left and middle lights work as normal for braking.

Also, not sure if this is connect but the right hand reverse light has stopped working, the bulb is fine as I have swapped it with the left hand one to check.

I know very little about cars, as you can probably tell. I haven't come across this problem anywhere else on the internet so wanted to check it out somewhere before I go to a garage and they give me 1001 expensive sounding problems when it could be an easy fix

thank you!

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Difficult that one. I would start by removing both the new brake light bulbs completely. If everything works normally (apart from the brake lights of course) then the problem lies with the bulbs. I think the bulbs are tail/brake light dual filament bulbs so the tail lights won't be on either. Check for the CD light, speedometer light and reverse lights and any other faults which ocurred with the bulbs in place.

If these are all OK then the bulbs may have been fitted the wrong way round. There are 2 bayonet pins at different heights and they MUST be fitted correctly so the 21w filament is connected to the brake light circuit and the 5w filament to the tail light circuit. Look carefully at the holders and you should be able to see which pin fits which slot.

Good luck!

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After reading your description of the strange symptoms, my initial thought was a poor or missing earth connection causing a feedback. Perhaps through the new bulbs being wrong or not properly fitted which is exactly what Ian has said !

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