I have a no start, no turning over with burning insulation on my 83 300D. I only get the burning with the key turned, but as of yet, have not found the short. With the battery connected, key off, I am unable jump the starter with any two combinations at the box. I am getting 12 volts to each of the large screws (#1, #2 in photo) in the junction box. The smaller screw (#3) shows a short to ground on each wire it connects. Is this typical of a failed starter or solenoid or do I need to try and jump the terminals on the starter itself? As you all know, everything is impossible to see.

Edit to add: I disconnected what I assume is the neutral safety switch connector under the dash and was able to bump the starter connecting terminal #2 and the wire #3. #4 I assume is going to the NSS which is likely where I have a short. Opinions on how best to proceed would be appreciated.

If it was the lavender/purple wire that smoked that goes to the glow plug relay. If that was the case that wire or something inside of the glow plug relay itself is what is shorted.

The White wire on the far right is the one that goes down to the Starter Solenoid.

However, in normal operation When the Key turned to crank the starter the voltage goes to the Neutral Safety Switch and on to a terminal on the Starter Solenoid that same terminal has the white wire that goes to the Junction Box and comes up from the Starter Solenoid to that white wire on the far right and gives voltage to the lavender/purple wire that goes to the glow plug relay and the effect is your glow plug relay is on during cranking.

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84 300D, 82 Volvo 244Gl Diesel

Since the white wire on the far right goes down to a terminal on the starter solenoid and that terminal is connected to wire wires inside of the Starter Solenoid it it is normal for that to be grounded.

You would need to remove the 2 wires from the small solenoid terminal to get at the circuit from the solenoid back to the neutral safety switch and on back to the Ignition switch. With that circuit if the key is in the cranking position you should get voltage at that wire.

If no voltage there can be a neutral safety switch and or starter bushing issue and or an Ignition Switch issue.

Since the lavender/violet wire goes to activate the glow plug relay that would also be normally to ground except that of course the wire is not supposed to burn.
That wire is only supposed to activate one of the relays inside of the glow plug relay not pull the full amperage that the glow plug relay uses.

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84 300D, 82 Volvo 244Gl Diesel

Thank you for explaining those circuits Diesel911. I am flying blind with only the Haynes wiring diagram, my MB manuals CD is packed who knows where. That lavender wire had been crudely spliced before I bought the car years ago. I replaced the crimp connection with a soldered splice with appropriate gauge wire. From what you explained, that had nothing to do with a no crank, no start, but neither did it resolve the short. I will keep looking for melted insulation.

I knew there were issues with the starting system before the no-start because occasionally the starter would remain engaged even after I released pressure on the key. I would get it to disengage by moving the shift lever into drive with my foot on the brake. I also have worn bushings in the transmission linkage, and a chronic blowing of the #14 fuse that I have never successfully traced to its cause.

I tried jumping the NSS from the 4-post connector under the dash with no luck. Maybe the issue is with the ignition switch as you mentioned. Thanks again for the help.

Frequently, the solenoid will fuse together, making the starter crank constantly. The short could well be in the solenoid as well. Drop the starter… I know, not a simple task, but a good place to start.

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Fuse number 14 has the back up lights. The Neutral Safety switch also turns the back up lights on and off.

There is a method to line up the neutral safety switch with the shift lever. I assume to index the switch properly.

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84 300D, 82 Volvo 244Gl Diesel

I'm assembling the tools needed to drop the starter. Vstech's post and my inability to locate melted wires anywhere else have convinced me it is the most likely source of my problems. I will try to clean up the transmission and check the bushings while I'm at it.

That braided fiber insulation on the starter wires, is it fiberglass or something else? Looks like I'm going to have my face in it, and I want to take reasonable precautions.

Just to see how this turns out .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

A quick read of a post on this thread. I might unplug the glow plug relay. Easy and takes no time. Not that probable as it should have taken the fuse in the relay. Yet some past owner may have bridged the fuse in the relay.

When you find evidence someone else had done things. Some things become possible. The starter is so much fun to pull on that model. I would figure out a a way to test it in place.

Thanks Barry. I disconnected the electrical connectors today and cleaned the crud off of the area as much as possible. I don't suppose it would hurt to test the starter in place now that I have it isolated.

Following as the 300SD has a mystery relay and fuse patched into that terminal block.

Michael

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Usta haves '69 250/8, '76 280C, 1971 250C 114.023, 1976 450SEL 116.033
Current have, 1983 300SD 126.120

About testing the starter in place, I was unable to get a jumper cable on to the large post due to the lack of clearance. My only option was to use 12-14ga. wire jumpers with alligator clips on both connections and then attached to a large screwdiver that I applied to the positive post of the battery. The negative post of the battery was grounded to the body as usual. I don't know if that supplied enough current to the starter. I got a click on the solenoid and lots of arcing but the solenoid did not engage. I assume the solenoid is indeed bad.

When I had what I thought were symptoms of a bad Solenoid one of our members suggested it was worn brushes. I was not convinced and ordered a new solenoid as well as a new bush kit.

When I got inside of the Starter I found the bushes were worn down to like 1/4th inch.

When I assembled the Starter I decided to re-use the solenoid. After over one year of use the old Solenoid worked perfectly.

The short story is just as the other member said it was in my case the bushes that were the issue.

If you get a brush kit be sure to get one with the metal tabs already on it.

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84 300D, 82 Volvo 244Gl Diesel

Note part of the problem with suspecting the Solenoid is that the Starter is usually difficult to get off due to the placement of the bolts and maybe the Allen heads on them.

That makes people think I had better replace the solenoid because I don't want to take the starter off again if the solenoid will not work after I thought I fixed it.

Since my Car is somewhat of a rust bucket I removed the forward covers and insulation so I could drill holes in the fire wall to get at the bolts (not entirely accurately).

So the starter had been working for over a year but I had to pull it off when I removed the Transmission to change the seals on it.
Having already drilled the holes in the fire wall was a huge help removing again.

Never-size on the threads of the starter bolts when you re-install it.

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84 300D, 82 Volvo 244Gl Diesel

Before taking the starter off the car one should always test both the solenoid and the starter proper by using a jumper to by pass the solenoid and see if the starter spins up freely and rapidly ~ this is dome by jumpering the two 13MM A.T.F. nuts on the end of the solenoid .

Worn brushes are certainly a common problem but I often find that simply taking the unit apart and cleaning and greasing it will make the starter proper work again for many more years .


A solenoid usually signals it's demise by hesitating to engage when you turn the key to the 'start' position .

There are a few different ways to break loose those pesky starter bolts, I have used an Allen wrench in the head of the bolt with a ring spanner over it and then a long cheater to provide the torque necessary to break it loose .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better