Won't Start.
 

Last week I did a diesel purge on my mom's 1986 300SDL (around 176k miles). It was running very nicely for about a week, until today. It won't crank. The instrument panel/coolant temperature will come up but when i turn the key one more notch to crank, it will just cut off everything, and no cranking will occur. I tested the battery's voltage, and it comes out around 12.3V. When I try to crank it, it will hold that same voltage. I checked the fuel lines and everything that I messed with during the diesel purge and they were fine. I guess it's an eletrical problem. Could this be a relay somewhere that went out? Or perhaps a fuse? I can't find the fusebox on the 603, i've only really poked around in my 617. Any ideas? As always, I appreciate any answers or advice. Thanks.

Definetely sounds electrical.

When my W123 starter died, I had the same symptoms, except a load drop when turning the key...no sound or movement at all.

If you turn the ignition switch to the start position and the lights go dim but nothing else happens:

1. Check the battery connections on buth ends of the cables.

2. LOAD test the battery-insuring that it first has 12.6 volts or more.

3. If these two did not solve your problem then the problem is the starter, but first ensure that you get power to the solenoid through the ignition switch start position.

The fuse box is right next to the master cylinder. I am not sure where the starter relay would be.

However try hitting the starter with a broom handle and see if anything happens.

I'm fairly convinced that the problem is one of the battery cables. Remove both cables from the battery and clean the inside of the clamps thoroughly with a wire brush and attempt to start it again.

If it repeats the same symptoms, then the positive connection on the starter needs the same treatment. Remove cable, clean thoroughly with wire brush, and reinstall.

Finally, check the ground connection from the engine to the battery. Again, remove the connector and clean it thoroughly and reinstall.

Bet it starts. :D

Hahahah. I was fiddling around for 'bout 45 minutes when I noticed my mom had left it in Drive. *slaps forehead* Thanks anyways, wow the responses came fast. Sorry to waste anyone's time =)

See, I told you that cleaning those cables would get it to go! ;)

I guess your nuetral safty switch is working just fine! :D