both brake lights out, 3rd working

[diyplumber1980]

Hi

Both my brake lights have gone out, but the third light works ok. I changed the bulbs but same problem. I have no idea what the fault could be. Has anyone come across this before?

Car is Seat Leon S, 2003 plate, 1.6 5 door. Petrol.

Thanks

 

[footprints]

Check the earthing to each bulb.

 

[diyplumber1980]

How do i do this? not really done much work on cars!

 

[footprints]

As a rule the wire going to the bulb is the live and the bulb holder is earthed.

you can try connecting one wire to one connection on the bulb and touching the other connection (usually the body of the bulb) to a clean bit of metal on the car.

If it lights the supply to the bulb is ok if it stops working when you put the bulb back in its holder the holder is not earthed correctly usually corrosion of some sort.

What sort of bulbs are they?

Bayonet fitting with one soldered connection on the base,
Bayonet fitting with two soldered connections on the base,
or capless just two bent wires coming out of the glass?

Are they just stop light or stop light and side light combined?

 

[diyplumber1980]

the wires are connected to the bulb holder with a push fit connector, bit like a mini scart connector. The bulbs were working fine last week, and the cars in good nick. I couldnt see any rust on the connectors.

The bulbs have only 1 soldered point at the bottom.

 

[Belle427]

The brake light switch fails on these but i cant remember if the high level light is wired seperately for safety reasons.
I will check the diagrams out and get back to you, unless someone comes back with an answer.

 

[footprints]

Sounds like ch427 has experience of this model, so may well be a common fault.
Otherwise try connecting the live to the contact on the bottom of the bulb and body of the bulb to good earth on the car.

You really need a multimeter if you are going to trace the fault.

 

[diyplumber1980]

Thanks for the replies lads, much appreciated. Ive got a multimeter. Could u advise how totrace rhe fault using this?

 

[Burnerman]

Clip one multimeter wire (set to more than 12v DC) to a definite known earth (metal point on the body shell), get someone to press the brake pedal whilst you touch the brass connector in the bulb holder centre with the other probe.
Personally I like to use a test lamp/screwdriver here to avoid spurious voltages, but thats how its done.
Are the other lamps in the clusters behaving themselves?
John

 

[diyplumber1980]

Thanks Burnerman. Yes, the other lights are all fine in that cluster of bulbs. The third high level brake light is also ok. Ive had a look online and a common cause im seeing is the brake switch on the brake pedal. Could that be the cause or would that knock out all 3 brake lights?

 

[Burnerman]

Sorry, I really can't comment on that one......that would mean that there would need to be two brake switches in the circuit - somewhat unusual I guess but possible! Maybe CH knows better.
Anyway, usually the high level lamp has its own earth so its not affected by the cluster.
Is there any possibility of removing the switch from the pedal area, and shorting out with a length of wire - or if you don't want to do that, its out with the multimeter to see what readings you get.
In one switch position the meter should read no contact, or infinite resistance - in the other position the meter should read 0 ohms.
John

 

[Belle427]

According to the diagrams the 3 lights are wired together so there must be a junction point somewhere.
The cable should be red/black from the brake light switch out to the lights, it may be worth checking the cables at the brake light switch first to see if any are loose or detached as its not clear where the junction point is.

 

[diyplumber1980]

Guys, i would like to sincerely apologise. I feel like a complete muppet. I took the car to garage today, and showed the guy the brake lights which were not working. I told him i changed the bulbs but it made no difference, to which he replied:

"well to be fair mate changing the reverse light bulbs wont make any difference to the brake lights......"

i was changing the wrong bulbs!

 

[Burnerman]

Classic We've all done it.....the trade secret is to either say nowt or blame it on something else - i.e blind the customer with science
John

 

[footprints]

Nice one! Thanks for letting us know.
I have done it with headlamp bulbs got the whole unit out and then can't remember which bulb is which had to put it all back to check