C Class Tail Lamp Warning??

[6C4GTS]

Guys - my 2004 MY C Class is giving me a dashboard warning saying to check the left tail lamp and saying that the back up bulb is on??

I've checked all the bulbs and they are fine.
I've swapped the bulbs for new ones.
I have looked for a back up bulb - what is this?
The warning is intermittent but annoying.

Any ideas - loose connection somewhere?

Thanks for any advice.

[Monkeylegend]

I think the rear light acts as a stoplight when the brake light bulb fails. If you see what I mean.

[va1o]

We've had this, IIRC if a bulb blows it will light up a different part of the unit instead... if that makes sense? Dealer fixed free of charge out of warranty, just needed a new bulb fitting to replace one which had blown.

[sussexjob]

My new shape c class has tail light problems, near side cluster started intermittently failing and finally gave up the ghost MB charged 300 squid, then 2 months later o/s starts playing up so investigated this a lot more and rear earth(brown) cable burnt out on cluster connection, looks like a design fault.