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  #1  
Old 09-02-2009, 10:40 PM
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How to Bypass/Test your Neutral Safety Switch

Lately it seems members are haveing a spat of no Cranking problems with their starters.
I was over snooping at another forum and found this Info that I have never read before concerning how to bypass/test your Neutral Safety Switch.
This Info Concerns a 1984 300D.
Testing for no Cranking; explanation from 240D3.OT mbworld.org.
http://www.mbworld.org/forums/diesel-forum/313982-no-crank-1984-300d.html
“First make sure the selector is in P or N. Cycle through all the gear positions and try in N.
In front of the battery is a small rectangular box. Use a jumper wire to jump from one of the large posts to the small post with the purple wire. If it cranks, you've got an issue with the neutral safety switch or the ignition switch.
Above the accelerator pedal is a 4-wire plug with a harness that runs down to under the accelerator pedal and to the transmission tunnel. Unplug it, jumper across the two purple wires in the female plug and try to start again. If it starts, you need a NSS.”
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Last edited by Diesel911; 09-02-2009 at 11:17 PM.
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  #2  
Old 09-02-2009, 10:48 PM
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And, depending on which year of which model, you may also have a wiring harness problem. I had to completely rebuild the connector and a foot or so of wiring harness on my '96 E300D (W210, OM606NA). The "environmentally friendly" insulation had turned to hard plastic and fallen off of the wires.
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  #3  
Old 09-02-2009, 11:15 PM
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Quote:
Originally Posted by Jeremy5848 View Post
And, depending on which year of which model, you may also have a wiring harness problem. I had to completely rebuild the connector and a foot or so of wiring harness on my '96 E300D (W210, OM606NA). The "environmentally friendly" insulation had turned to hard plastic and fallen off of the wires.
Thanks, I will correct the above and ad the year and model. But, I cannot change the title.
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Old 09-03-2009, 03:00 AM
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I had to start my 85 300D with that teminal a couple times when the NSS went south.

the plug above the accerator peddle has 4 wires. purple are the start.

I think the other 2 are black with a red stripe. those are the back up lights.

Charlie
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Anyone that thinks a 240D is slow drives too fast.

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  #5  
Old 09-03-2009, 10:06 AM
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Good piece of information there on jumping the NSS. Not all 123's have the terminal block in front of the battery to bypass the ignition switch. On 116's the terminal block is under the battery.
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  #6  
Old 09-03-2009, 01:29 PM
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Quote:
Originally Posted by kerry View Post
Good piece of information there on jumping the NSS. Not all 123's have the terminal block in front of the battery to bypass the ignition switch. On 116's the terminal block is under the battery.
The guy from the other forum used to post here also. His Avitar is VGT in a square.
What suprised me is that I did not read the info on this forum.
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  #7  
Old 09-03-2009, 01:39 PM
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this wont work on my 77 so thats why I make sure I have a good NSS
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  #8  
Old 03-27-2010, 05:59 PM
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As this just helped me out and came up nearly first in my search for such a thing, I thought I would add to it. For my 81 300 SD this switch was found behind the carpet side panel next to the accelerator pedal, so you have to take that off to get to it. Also it is a 6 pin plug on the SD not a 4 pin but it is still two purple wires , which I had to take apart the plug to find out it is the top two ports.
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Old 03-28-2010, 01:43 AM
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Iam sure this terminal block could be added to the cars that did not come with them. I have pulled a couple off junkers at PNP. was thinking of putting one on the 240D.
In the picture below, the block has a cover, this one seem to be missing.

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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

http://i30.photobucket.com/albums/c3...ilys/boobs.gif


Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works
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  #10  
Old 06-16-2010, 02:39 PM
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Neutral Safety switch bypass...

I went to leave for lunch, turned the key and no crank. I am pretty sure it is the neutral safety switch because of prior issues with it, but I need to start the car to get it home. I looked for the terminal by the battery to try starting it but I can't find it. Where is the terminal on the 87 300D? Or, where is the one with the two purple wires to bypass the NSS? Thanks!
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  #11  
Old 06-16-2010, 03:20 PM
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Quote:
Originally Posted by mkrazy1 View Post
I went to leave for lunch, turned the key and no crank. I am pretty sure it is the neutral safety switch because of prior issues with it, but I need to start the car to get it home. I looked for the terminal by the battery to try starting it but I can't find it. Where is the terminal on the 87 300D? Or, where is the one with the two purple wires to bypass the NSS? Thanks!
Unfortunately this Thread does not apply to your model and year.

It would take looking at the wiring diagram for your year and model to find out where you could tap in to bypass the NSS.

In general if you want to crank the Engine on any Engien with an Electric Starter you will have to locate the Terminal on the starter Solenoid where the Wire coming from the Ignition Switch goes and connect that to a source of Positive Voltage. This is best done with a Remote Starter Button with Alligator Clips on it.

On some Gasoline Engined Cars you need to have the Ignition Switch ON when you crank the Starter this way or it causes some electrical problems (I do not know the exact details on that I just remember reading the warning years ago).
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  #12  
Old 10-18-2013, 12:32 PM
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Where is the starter terminal block for 87 MB 300sd? How do I bypass NSS?
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  #13  
Old 10-18-2013, 08:11 PM
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Quote:
Originally Posted by forestbeach View Post
Where is the starter terminal block for 87 MB 300sd? How do I bypass NSS?
I have been told this Wire Junction/Terminal Box is under the Battery Tray. This is where you can jump the Starter and get Starter to crank. Use proper precautions when doing that.

The other pic shows that the Electrical Connector on the W126 is close to the same location as it is on the W123. However, I don't know if the Wire Colors are the same.
Attached Thumbnails
How to Bypass/Test your Neutral Safety Switch-terminal-block-sd-jump-start-blow-up-oct-13-m.jpg   How to Bypass/Test your Neutral Safety Switch-w126-neutral-safety-switch-connector-oct-13.jpg  
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  #14  
Old 10-19-2013, 02:18 PM
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Angry Bypass NSS 87 MB 300D

I found the terminal block in front of the battery in my 87 MB 300d. But when I tried to connect one of these terminals to the positive pole of the battery , nothing happened no crank(even I turned the ignition key on). The starter of 87 MB 300d may not connect to this terminal block like older MB(it worked for 85 MB 300TD and 80 MB 300D). Please help.
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  #15  
Old 10-19-2013, 07:59 PM
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Quote:
Originally Posted by forestbeach View Post
I found the terminal block in front of the battery in my 87 MB 300d. But when I tried to connect one of these terminals to the positive pole of the battery , nothing happened no crank(even I turned the ignition key on). The starter of 87 MB 300d may not connect to this terminal block like older MB(it worked for 85 MB 300TD and 80 MB 300D). Please help.
Someone with a W126 will have to chime in.

The old method when there is no nice Wire Terminal Block to use is to go from run a Jumper Wire or better a Remote Starter Switch from the Positive Battery Terminal (or another source like the Large Cable on the Starter) directly to the small terminal on the Starter Solenoid.

If that does not activate the Solenoid and crank the Starter your Solenoid is no good or there is not a good Ground.
If you hear the Starter Solenoid give a healthy loud click but the Starter does not crank you likely have some internal Starter issue line worn Brushes or the Contact inside of the Solenoid that connects the Voltage to the Starter is burned up.
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