Here's the scenario:
My 1992 500sl wouldn't start. The engine would crank but
wouldn't start. I noticed with the key turned to the final on position,
only the srs light was lit-no other idiots lights were on(which they should
befor the engine crank). The windows would not operate either.
after numerous attempts to start the car-i called mercedes roadside
assistance. Before they called me back, I checked fuses-no problem.
I finally turned the hey to full on-waited 20 secs, noticed that
the idiot lights finally came on cranked the engine-it started! I got
the car home but have been unable to start it. any ideas would be
appreciated. the car has 97K miles.

Follow up to my previous post. Problem was diagnosed and resolved by replacing the ignition switch. $97 part +3 hrs labor. This also solved my intermittent ASR dash inicator "light-on" problem.

My 96 sl won't start this week either, how did you get it diagnosed for the ignition switch?

Ignition switch because ignition circuit was not engaging; the coils were not receiving power, and the idiot lights were not coming on (starting is a separate part of the ignition circuit). On the pre-mass airflow systems ('92 and earlier), starting ether goes a long way in testing if the ignition circuit is energized (EZ does it, or you'll start the car on fire), but so does a voltmeter or scope. On a post-'92 with MAF sensor, if your blower motor doesn't engage and your fuel pump doesn't cycle, ignition switch is a likely culprit

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You'll need to be much more specific on your starting problem if you want help diagnosing it (turns over but doesn't start, doesn't turn over, etc.).

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Don't ask me, I'm a shop-owner by default