My wife has a Mercedes 300 SL (W129). The left hand turn indicator lights of its own free will! The indicator light on the dash and the external lights will even stay on after the ignition is turned off!
I have a clifford alarm on it which still flashes all the indicators.
The stalk has no effect when the light is stuck on, but works correctly when it is not and the hazards work correctly.
The dealer has had a look but cannot find any fault as it did not perform for him.
He has tried disconnecting the alarm from the indicators, but the problem still occurs.
The original factory alarm was disconnected very recently.