I couldnt start my engine today using keyed ignition. I had a brain storm.
Leaving the ignition key in run mode, I got some wire and did a hand fire from the battery +12V post to the starter solenoid contact and the engine started.(Solenoid is okay)
The Wiring Diagram shows the only thing that can go bad in this case is the Ignition Switch. Is that true, save for a dead wire somewhere? Does the ignition switch normally go bad after only 20 years in a Mercedes? There are no relays in my 123CD wiring diagram.
Any other possibilitys?
What is the cost and lag time for ordering a new ignition switch with a matched key and VIN number?

Ya, only 20 years, that's about right. I'd check the neutral safety switch, too, that would keep your crank sigbal fron the solenoid also. Try holding the key in "start" while moving the shifter through the gears, see if it cranks at some point in the quadrant.....Gilly

You should also check the nylon bushings on the linkage from the gear shift lever to the transmission.
Bill Lewallen; Lexington,Ky.

Yep, good one Bill, I've seen this several times also....Gilly

Gilley B,
Whether it's the neutral/safety switch or the nylon bushings, it's a job I never liked doing. Glad it't Cars Meow's problem and not mine,but I'm sure he will fix the problem.
Bill Lewallen; Lexington,Ky. Home of dumb asses and fast horses..

Why check the nylon bushings?
 

Is this becuase if they are oit of alignment they will affect the neutral start switch positioning with repect to
the neutral position/? I replace my linkages and bushings last year when i rebuilt the motor. Thanks

Well, sort of out of alignment. The transmission selector lever on the transmission won't be in the proper position relative to the shift rod. The bushing is thick enough that the transmission lever (in the car) will be in park, but the selector lever on the transmission won't be fully iin park, and consequently the neutral safety switch won't be fully in park either, so it's sort of like trying to start the engine in reverse, the neutral safety switch will prevent the crank signal from reaching the starter solenoid. Usually you can tell the bushing is worn out both by the problem you described, and also you can hear the shift rod making a sort of clinking sound when changing gears (moving automatic shifter into different gears).....Gilly from Wisconsin, Home of beer farts, leaky motorcycles and Americas Ace of Aces, Dick Bong

Cars Meow,
If your car has the terminal block on the right(pass) side inner fender, find the purple wire and use a jumper wire from it to the + battery term. If you don't have the terminal block, don't despair. We have other ways to get your starter working.Look in front of your battery for a plastic sheath of wires. Slit the plastic for about one or two inches, and reach in and get the purple wire. Skin back enough of the insulation so you can connect your jumper wire. If you want to start your car, make sure it is in park or neutral because you are by-passing everything.Let the glow plugs glow for a while before engaging the starter.
I have all three of my Mercedes diesels wired with this jumper wire. Comes in handy when adjusting the valves and you need to turn the engine over. Good luck..
Bill Lewallen;Lexington,Ky.Home of fast horses and dumb asses.

Is there really a neutral switch?(manual trans.)
 

83 240D Manual transmission, sometimes the car stll starts! Today i got in absent mindedly and it fired right up! Other times I must still jumper the solenoid.

Is there really a neutral switch?

The service CD wiring diagram shows the wire going straight from keyed ignition to starter, I see no neutral switch! I'm going to work on it at the crack of dawn tomorrow.

On my 123 1981 280E, there was a neutral swith, AND there is a combination AC/Starter relay. I believe that it cuts the compressor clutch power when cranking, but if it goes TU, the starter does not get power.

You might look for this on your 300 TD.