300D Won't Start

Sep 29, 2008 4 Replies

My '77 300D which usually runs great wouldn't start this morning. I tried jump starting it from my wife's car and it still wouldn't start. Electric clock, lights, etc., seem to have normal brightness. Mercedes battery is only a year or so old. Glow plug indicator light on dash does not come on. Also, engine will not crank. Is there a fuse or something I should check or replace?



Many thanks,



Peter Hollings


You got a couple of issues...

  1. As for your ignition switch... when you put it to start position... does it feel like normal? With all that tensions or is it weak?

  1. Glow plugs... you got one or two glow plugs burnt out. Disconnect the wire and use ohmmeter to figure out which one is bad. You might consider switching to modern pencil type kit if you still have that big resistor setup.

  2. If the ignition switch is good, then try setting your gear to neutral to see if it cranks... if no go, then get a hammer and whack your starter a couple of times to see if you can crank it after hitting it... if yes, then starter is shot too.

Let's assume the 1 year old battery IS OK. The fact that the motor doesn't crank AND that the glow plug light is dead implies a circuit or an ignition switch problem - that neither the starter nor the G.P. system is receiving power.

Suggest you first focus on the ignition switch - make multiple tries before investigating the electrical (hot & ground) circuits from the battery to the chassis and chassis to the engine.

A further thought: Be sure the battery is really a good one; jump it from another car (+ to +, - to -) to be sure the problem is with your car and not your battery.

Always first suspect the most obvious, there's always time later for the complicated stuff.

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