W204 Rear Light Burnout

Landie1

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After thinking i had cured my rear light problem last weekend prooved otherwise so I have purchased the rear bulb mount, plug and terminals for both sides from Ebay (MB Grimsby). I know its the brown earth wire that burns out. My questions are...
What causes the problem in the first place as i dont want to fit new parts and the same happen again, and
If it is just wire gauge too small do i need to connect the original brown earth wire (i.e would it upset the canbus if the original earth is not connected) or can i use a seperate larger gauge earth wire direct to the bodywork.

I hope that all makes sense

Thanks
 

Ted

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The reason they burn out is that the connection and wire gauge are not up to handling the current with all lamps on e.g. sitting at the lights with sidelights on, foot on the brake and indicators on. (the supply wiring is fine but of course all of the return current flows through a single cable)
over time this causes the bad connection to get worse and worse as the connection and wiring around it degrades due to the heat generated.
it won’t affect the canbus if you use a larger wire gauge - it will be an improvement - also make sure that your connections are clean and making good contact.
 
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Landie1

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Thanks for that. I'll look at it at the weekend and let you know how it goes.
 
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Landie1

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So after fitting the new rear bulb mounts it turns out you do need to use the original brown earth as the canbus needs an earth signal. I tried with a seperate earth wire but had no rear lights. I did crimp and then solder the connections to ensure the best connection possible so hopefully that will make them last longer. By the way the kits were £22 each and included the bulb mount, bulbs, new plug and 2 connector pins.
 
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