Intermittent turn signal failure (1985 380SL)

[Southin]

On occasion I find I have no turn signal response in either direction (no ticking, no flashing indicator lights, no front or rear turn signals). However, if I turn off the ignition and restart the car, usually everything returns to normal. What can cause this and how can I fix it? It doesn't appear to be a faulty turn signal stalk, since if the turn signal doesn't work, no amount of jiggling the stalk will reactivate it...but restarting the car usually does.