Citroen C3 int. l/h rear indicator

If car not used a lot or for short journeys , battery may be low which can cause this type of problem .or an older battery If that's the case charge , test or replace if needed.If the indicator is not working , test bulb , test for power at bulb .holder .If both o.k try temp earth wire to lamp / bulb.

I have a feeling there may be modified bulb holders and a new earth strap for this fault

I have rectified the problem, it is indeed an earthing problem caused by the common earth pin in the rear light clusters becoming corroded. When you think about it this tiny pin passes all the current through a light cluster which can be many amps if side/brake/fog/indicator are all on at the same time{possible}. This is poor design by Citroen. I cured the problem by soldering a wire to the common earth plate in the cluster,drilling a hole to allow the wire to pass behind {don't thread the wire through the existing small holes- these are spark gaps which have sharp points an can pierce the wire. cut the wiring loom earth wire{green/yellow} close to the plug then use a small connector to connect the loom earth to your new wire. Do both lamp clusters! Problem solved. Happy Motoring

Good you got it fixed , thanks for updating the forum , may help others .