[MBZ] 300SD starts sporadically

[Dennis Perkins]

This weekend I went out to my car, an 84 300SD and when I turned the key I 
got nothing.  I have a new battery in it.  The headlights did not dim when I 
turned the key and I was able to start the car by turning on the ignition 
and jumping across the terminals in the box on the passenger side of the car 
under the hood.  The next time I tried to start the car it started okay. 
Now I have to trace what is the problem the next time it happens.  My 
question is when I jump the car through the box under the hood does that 
bypass the ignition switch?  I'm thinking that it must be either the 
ignition switch or the starter lockout switch on the transmission.

Any help would be appreciated.
Dennis Perkins
84 300SD