Ok, we have a 1993 Mercedes 190E model, believe it is the 2.3 L. About
3 months ago it quit while someone was driving it. So it was parked
while we found time to work on it, we tried starting it one evening and
it fired up fine, ran for five minutes and then quit. It has not
started since, it does crank. We have done the following and are out of
ideas:

Changed the distributor cap
New rotor button
New coil
New crank sensor

The problem we have narrowed down to after all of this is that it is
still not getting spark/fire to the plugs. I have tested to see if it
has an alarm (by locking doors with window down, from outside with a
key, reach in pulled the plunger and opened the door. Also tried just
pulling the inside handle, neither time did the alarm go off if it has
one), assuming it does we've been told this could be the problem. Thing
is, we don't know where it is located or what to check on it. Also,
assuming it doesn't have a security system, what else could be the
cause? Please post any ideas, as we are near taking it to a mechanic
and would rather not cough up all the $$$. Thanks!