Last year my car did something very similar. When I would activate the turn signals nothing would happen, although unlike you my flashers would not work either. I traced the problem to the combination relay in the back of the fuse box. One of the pins had a crack in the solder. I soldered the bad connection and haven’t had a problem since. It may not be your problem but it’s worth checking.

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'94 E320 with 272,000 miles. '92 500SEL 133,000 miles.
Mods to the '94: TomTom GPS in place of ash tray, Auto Dimming Mirror ,Memory seat, DEI 545T Auto lamps, DEI 530T Auto Up/Down Windows, DEI Remote Start, Motorola Bluetooth® Car Kit, Built in phone charger using factory phone wiring, RainTracker Rain sensing wiper, Keyless Entry, Ambient lighting of center storage compartment. Soon: factory heated seats, REST
Mercedes-Benz is my addiction of choice.
http://www.youtube.com/vanwiek