300tdi 1998.cant get rear brake lights to work.the one in the rear door is fine but sides dont work.i checked bulbs wiring fuses etc but cant track down problem.if the brake switch was in any way faulty would it light the rear door brake light and not the sides.need help thanks.electrics drive me mad.

stevenacia said:

300tdi 1998.cant get rear brake lights to work.the one in the rear door is fine but sides dont work.i checked bulbs wiring fuses etc but cant track down problem.if the brake switch was in any way faulty would it light the rear door brake light and not the sides.need help thanks.electrics drive me mad.

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As you say if the reverse switch was faulty the rear door light wouldn't work.
From what you describe I'd be looking at the bulb holders .
Try taking off the drivers side rear light cluster. Two white plastic wing nuts in beside bulbs accessed thro panel in boot.
Try wiggling bulb about while someone holds brake pedal down you may get it to light.
Check the bulb holder for any signs of corrosion/white powder. Clean holder with emery. Also check if the bottom centre contact actually touches the bottom contact on the bulb.
If still no joy follow wiring back to connectors and check connectors for corrosion.
The earths should be checked, follow black wire to where it is bolted to body.
Unbolt and clean to bright metal and re-assemble.
If all this fails you need a test meter to check for voltage and earth at the bulb holder.
If you get one side working do the same to other side.
Hope this helps

thanks i ll check that. if one side doesnt work would that stop the other side working if the problem is what you are describing.

stevenacia said:

thanks i ll check that. if one side doesnt work would that stop the other side working if the problem is what you are describing.

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The reason I suggest looking for a fault in the offside light cluster is because your door brake light is operating and the wiring for that is connected in behind the rear light. Therefore you have a switching voltage from your brake light circuit in that area, in a connector somewhere. Why that voltage isn't getting to your brake lights is the problem, if it is getting to the brake light fitting it suggests the earth is faulty.
If there is a faulty connection in that position it could well put off other side.
I'm afraid it is a case of systematically working thro the problem.

It your number plate lamp working as it uses the same earth connection a RH tail lamp and I think there's only earth connection per tail lamp unit so if the earth was iffy then the whole lamp would be down.

I replace a tail/stop lamp bulb once took half hour to get to it 5 minutes to ghange the bulb and another half hour getting it working with the baynet bulb holders that are very iffy. You can fit the bulb holder the wrong way round then the bulb doesn't work.

i had a similar problem last year,
i traced it back to the light cluster, the side light buld would not work even though there was voltage to it.
take out the bulb and use some fine sand paper to clean the metal where the bulb locks into and also the metal strips where the loom plug plugs onto the light cluster. this cured my problem but it took some working out

thanks.time to get my detective skills.pain in the arse.