Front indicator stuck on

I have a 2004 L322 which will not turn of the front nearside indicator. The bulb is permenantly iluminated even with the key out of the ignition and the car locked. Side indictor and rear work as normal so it can't be the relay(i think). I have no warnings on the dash indicating any faults. Any ideas?
Thanks

Sounds like it's dragging power from a live feed somewhere. Start tracing the wires out one by one, look for damp sockets, connectors, damaged insulation etc