Its been a while since I have needed to post anything on here, but this one is a write-up of how I solved my problem - may come in handy for anyone else.
My car is Audi A4 Avant B7 140tdi (BRE engine) 2007. 158k miles.
The fault/problem
Yellow warning lights come up on the dash saying rear left tail light bulb failure.
Upon checking the bulb, it is sound, and works on the opposite side.
Checking the connector and I find this:
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The 4th slot seems to have been charred. Checking the pin end on the back of the light cluster and I find this:
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The 4th pin is charred/corroded. This is an earth pin and (I think) due to high resistance somewhere, this has corroded. Someone with more electrical knowledge than me can correct me please.
The fix
My fix (bodge) is to bypass the earth. I soldered (badly I know) the thinnest multi-stand copper wire I could find onto the earth bar on the inside of the light cluster:
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I ran the wire out through the hole reserved for ventilation
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Next, I snipped off the wire from the connector end and soldered a spade connector and made the connection to the wire coming out of my light cluster.
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Wrapped some electrical tape around the joint and it's been working fine for the past 5 months.
I do not recommend the blue tack as it completely stops the ventilation, I have removed mine after condensation build up.
Now I have the RH to do as the same error is annoying me on the dash.
Here' s a pic of the light clusters and PNR's involved. Hope this write-up helps someone.
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Has anybody found a better way to do this? Would love to know.