Ken,

Connect a wire to the solonoid screw that connects to the wire to the key switch. When turning the key doesn't work, touch this wire to the + battery terminal.

If this gets the starter to work every time, the starter and solonoid are OK and the problem is either the key switch or something between the solonoid and the key switch.

You should get a wiring diagram of your model so you can see just what is between the key switch and the solonoid.

P E H

Well said, PEH I am glad you jonied back in this discussion, I'd hate to see
kchristopher buy a new starter and go thru all the (ugh!) work to install it then find he still has a problem! I still have a ache in my arm where I pulled a muscle after changing a starter motor last year.

I still bet its the neutral switch.
One way to test these things is to put a small 12V bulb connected to two leads across the contacts, the leads can be small wires and long enough to bring the lamp into the car thru a window or something while you work. The bulb should not light when the key is turned to start. If it lights then the contacts are not "made" at that particular switch.

Say, I have to put my foot in my mouth for saying there is a reverse sense switch in the manual tranny cars. Duh!
My friend has a manual 300D W123 and I know it can be started in gear, I accidentally did that so I have to say I goofed when I said the manual trans used a reverse sensing switch. It does however have a backup light switch, that is what I saw when I had the rubber boot off.
DDH

__________________
'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

I suspect it is wireing, but I'm really curious as to why, after replacing the first solenoid, it immediately worked fine for a month and a half.

New key switch is $100 from the dealer. Are they the only source? Might take the switch out and look/clean inside.

Talk to a lot of people before you just 'take the switch out'. From what I have heard there is considerablely more to the job than there seems.

Take out your instrument panel. Its dead easy. If you have a manual oil pressure guage plug it ASAP. Don't just stick a match stick in the end but get a threaded fitting that will seal it. Otherwise when you accidentiially start the car, which you will, you will not only fill your shoes but most of the driver's floor pan and back of the insrtument panel with oil. The really black Diesel kind of oil.

Pull the plug out of the back of the ignition switch. The plug has numbers at each hole. Connect a jumper(small alligator clips will fit into the holes) from hole no. 30 (either one-there are 2 of them) to the corresponding pin on the ignition switch. This will bring power to the switch.

Now jumper hole and pin no. 15. This is the wire that takes power to the no. 3 terminal on the ac starter relay when you turn the ignition switch to the no. 2 position. Read my previous post about this relay. With a volt meter or just a wire you can touch a ground at the no.3 hole in the starter relay and get a reading. If you jump this no. 3 wire to the no. 1 wire at the relay plug your starter should kick in.

Back to the ignit. switch. Find the pin on the back of the ignit. switch that corresponds to plug hole no. 50. You'll have to count around the back of the switch and find the pin by feel since you can't see back there. If you attach a jumper to no. 50 pin and turn the ignit. switch to start you should get power from your jumper.

Next connect the other end of that jumper to the no. 50 hole in the ingit. plug. Get someone to hold the ingit. switch in the start position. You should get power to no. 4 wire at the ac start relay.

If you have power at the no. 4 hole plug in the start relay take the back off the plug. It just pops off. Now if you touch a jumper from the no. 4 pin in the back of the plug to ground not only should you feel the relay click in but your starter should also kick in. By doing the above you have bypassed the trans. safety switch. This will enable you to test all the components of the starter relay circuit.

From what I have just been through, as I mentioned in my earlier note to you, I would check for a ground fault first. If you have put in a new solinoid and it stopped working after 6 months I would look at something other than the solinoid, esp. since you can jump it with a screwdriver. The solinoid in my car is 30 years old and still going.

Dang thing started working again tonight while running errands around town. Must of started 10 times without problems. This is going to make dianosis a little more difficult

Chris,

Intermittent problems are always hard to find.

P E H

the electric part of the switch was lose and missing a screw ...... simple thing to do
1 pull out insrament cluster
2 look at the electric part of the switch
3 if lose tighten if not
4 take off "the electric part of the switch"
you don't have to remove the tumbler, just get a stubby 'Philips? " i think
5 once removed plug the plug back in and
turn the key all the way,and turn the center electric part carefully with a flathead if it feels lose it's probbly bad
hopefully you get the idea ...i'm half awake hope this helps
jason

I had already pulled the chrome ring off the key switch and started studying the key lock and stuff behind it when I decided to just replace the starter.... then PEH described how the electrical route inside the starter but before it gets to the solinoid could cause this type of intermittant problems.... then when they opened up the Starter they showed me the arcing at the bolts inside which hold the brush frame in place... the actual brushes were in great shape..... they even mentioned how robust a set of brushes MB puts into these starters....

Okay, so it was working fine all weekend. Therefore, late yesterday I decided to remove the key cylinder to see how it worked, what was behind it, if it could be cleaned, etc.

Using instructions found on another thread, I turned the key to the first indent, inserted a 1.3mm allen wrench in the hole around the perimeter and tried for a good 3 minutes to remove the cylinder. Multiple times. No luck. However, the last time I tried, I almost couldn't get the key to turn back off. Finally did and now the cylinder turns freely as it did before (sometimes you have to jiggle the key a bit to get it to turn).

This morning, my efforts were rewarded with a no-crank situation. This would seem to point to the key cylinder, I suppose, since nothing else was 'messed with'.

So, I still need to remove the key cylinder. I've found some better instructions (finally found the section in the manual), so I'll try it again. Should I wait until the new cylinder lock gets in before attempting again? Don't want to tempt fate much.

The car was going to be a keeper (built it from two cars with opposite problems), but the girl next door fell in love with it and wants it for her first car. Now the plan is to fix this problem and sell it to her. Don't know how long before I get into another diesel benz, so I've not purchased a good manual. (Probably start looking for a 300 turbo, but you never know what pops up around here. Can't be picky unless willing to travel.) Thanks a bunch for all the help you all have given.

If you put two cars together... do you have a spare starter you could put into it just to check out my theory ?

The other starter has a busted nose. Casualty of the thrown rod in the original 4 cylinder. In my original solenoid replacement, I started by attempting to remove the starter and couldn't get the bolts loose. Discovering that it could be easily changed from topside, I never went back below. Knowing how tight those things are, I don't want to think about having to actually replace the starter.

"I don't want to think about having to actually replace the starter."

I wish mechanicing worked like that....you might want to use logical diagnosis to determine what you work on... if you want to actually solve the problem...

Re define the problem as figuring out how to get those things unstuck...

Then be religous about using AntiSieze on all threads which you replace on all vehicles from NOW ON..... that way a bolt or nut can only be a problem ONCE in your life....and the number of bolts and nuts in your life IS a finite number... so after a while you are home free....

The easiest, but unavailable solution would be for the person who put it together to use less than 300# of torque when installing.

Like I said, I tried but then realized I didn't have to mess with it, so I stopped thinking about it. If it came to it, I could come up with a method.

Already standard operating procedure. Learned that lesson many years ago. This should be the second thing taught in mechanics school, and the second purchase made my an aspiring mechanic - right after tools.

"I tried but then realized I didn't have to mess with it,"

This is what I fear is not correct.... hate to see you mess with the key switch if it is the starter body which is the problem... I wonder if your desire not to have to deal with those stuck bolts is affecting your diagnosing conclusions....

Christopher,

Before you tear into the switch try pulling the plug off the back and jumping the circuits to see if the car starts. If you can start it w/o the switch then the switch is the problem. If you can't then the problem might lie further down the line.

First law of mechanics, "Check the easy stuff first".