SLK 1999 intermittent ignition problem

1999 Mercedes SLK 230. Intermittent problem where the car just dies and will not crank when you turn on the ignition. All the idiot lights light up as they would when you first turn on the ignition but the car will simply not crank for a couple of minutes, or several minutes and once overnight - but the next morning it started right up. Sometimes this occurs when the engine is warm, sometimes when the car has been sitting and the engine is cold. Everything else works, lights, windows, etc., when the car won?t crank. Brought it to two places and ran diagnostics - but since the car is running okay at that time nothing shows up. My mechanic thinks it might be related to the engine disabler function but does not have the capability to test this.

 Do you mean the engine dies as you're driving along or just won't crank after you've shut it off?  If it just doesn't make any noise when you turn the key to the start position, it could be a problem with the neutral safety switch.  I don't know if this particular car has a traditional neutral safety switch, but it will have something that prevents the car from starting if it's not in park or neutral.  You could try moving the gearshift to neutral or jiggling the gearshift when you try to start it.  Other possibilities:  Poor battery cable connections either at the battery or starter; The starter itself may have a poor internal connection (dead spot) that is intermittent, which would require replacing the starter.

There may be an intermittent problem with the ignition switch causing this to happen. I would check for an intermittent power source that involves the starter circuit and the ignition areas.