There is always something going on
 

My 300SD was working fine all day yesterday went out last night to run to the store turned the key and NOTHING. Now I have something to do today. Any suggestions where to start.

Battery's possible, as is the alternator. These diesels don't require any electricity to work once they're running, so it's entirely feasible that you had enough power to start last time but the battery was too drained to get another start, even though the engine was running fine...

I'd get the battery tested first, then see if there's a draw with everything shut off...if the battery's okay and you're not getting a draw (or only a tiny one i.e. radio memory, clock, etc), I'd suspect the voltage regulator.

Just some thoughts...good luck!

After checking everything mentioned in the previous post, and checking all connections (at the battery, at the chassis grounds, at the starter, etc.) and if all checks o.k., you might also check the neutral safety switch. Good luck.

Battery seems to be good it read over 12. all electrical items work. Glow plug light comes on. It is the last turn of the key to start the engine is where there is nothing. I am not good with electrical repairs so anyone that could guide me through it I would appreciate it. Beautiful day in NJ so I would like to get the problem diagnosed. My novice experience I would like to know how to test the starter.

Does it click or anything? Sounds like a bad solenoid on the starter or a short in the wire between there and the key to me. If you could get to the starter you could use a screwdriver or something to bypass the solenoid and kick the starter over.... but I doubt you can get in there (be careful when trying this, make sure you're in park). Hopefully someone else will have a better idea. Double check the connections around the starter too.

No click just dead. I found a damaged wire going to the alternator and repaired it but it didnot correct the problem. The starter looks like a bear to remove.

You have nothing? No dash lights at all? Completely dead or just no crank? Do the lights work? Do the lights dim when you crank?

All of the lights work and all of the accessories including the glow plug light and the buzzer indiczting I do not have my seatbelt on. There is nothing when I turn the key the last part of the turn to start the engine after the glow plug light goes out.

Does your tach go crazy and jump around when you try and start it? Do you hear a strange noise you've never heard before? Do things flash and flicker? If they do, it has something to do with the battery.

Alex

No, Nothing like that happens. There is nothing. Could it be my solinoid?

If lights are stong but no response when starting, check the neutral safety switch. Try starting in Neutral or push the shifter foward in Park while starting. But even if that doesn't work it could still be the switch. When mine went in the 190E nothing could coax a start out of it.

dpbrowne,

There are a couple of potential places where you are losing contact. One would be the connections to the starter itself. If you are not getting a "clicking" noise when you move the key to the "start" position, I would start the investigation assuming the solenoid is not getting power.

A week or so ago I went through a troubleshooting exercise assuming power was not getting to the glow plugs on someone's car, and sent them on a search and destroy mission that was probably unnecessary. Apparently the glow plug relay died, so addressing sending power to the relay was not necessary. This time I would recommend you confirm power is getting to the solenoid first.

When you look at the front end of the starter you will see a couple of wires connected to the starter. I am describing this purely by memory as I am not at home at the moment, so you may have to interpolate my descriptions with the reality of what you see looking under the hood. The one on the smaller, outboard body bulge is the connection to the solenoid. It should have a little rubber boot that covers the connector after it is made, but the wire itself has a purple stripe on it I think. It is a smaller wire. The thick one is the connection from the battery to the starter motor.

The solenoid is a linear displacement type device that engages the pinion gear on the starter with the ring gear on the flywheel, and, once it is fully extended and the gears engaged, it becomes a relay to energize the starter. When you let go of the key, the power to the solenoid stops and a spring pushes the pinion gear shaft back into the starter body bulge (sometimes a separate, smaller body bolted on to the starter body). With a low battery charge, or not enough travel, you get the clicking noise as the linear motion out and back is cycled by the key switch. If you are not getting the clicking the chances are you are not getting power to the solenoid.

You can check this by having someone try to start the car while you hold the probes of a multi-meter on the screw holding the wire to the solenoid and the engine block. You should set the meter to Volts, in the zero to 20 Volt range or so, and look for 12 Volts. If you have no Voltage with the key turned to "start" you need to check the power circuit to the solenoid. I am not at home and cannot remember this circuit exactly, but I believe the power comes from the battery to the light switch and from there to the starter key and from there to the solenoid. It is not uncommon for the key's electrical connectors to fail, and I have heard of a few light switches failing. These connections are accessible from under the dash.

If you are getting power to the solenoid and it is not snapping into the start position, you need a new solenoid as a minimum. I would get a new starter from Fastlane, and get the heavy duty one.

There are past posts with very detailed instructions on how to get to the key switch and change the electrical switch out that is connected to the back.

Given your other electrical stuff works, I think the light switch is an unlikely culprit as, I recall the power to the fuse box comes from the same connector on the light switch.

Good luck and I hope this helps. Jim

Thank you fopr your advice. I have a few more things to do at the office this morning so right after lunch I will get to work on it (Sometimes having your office at home is a blessing). The solonoid seems to be on top of the starter. If the solonoid is bad can that be replaced independently without changing the starter?

maybe try this first?
 

try smacking the starter with a hammer and then try the key again.
sometimes the solenoid gets 'stuck'

Solenoid replacement is not too tough
 

I did it on my 1983 300SD - check my site.