Neutral Safety Switch Troubleshooting 84 300D
 

I was having no Starter Motor Cranking issue.
Another Member had posted this info: 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.”
However, the Instructions will tell you if your Neutral Safety Switch is bad but not if it is the Ignition Switch causing the problem.
But, I had never seen that connector or actually done the test.
Pic one shows where the Neutral Safety Switch and the Backup Light Connector is located.
Pic 1 one the location of the Connector.

Pic 2 is a close up of the Connector

Pic 3 is the Connector unplugged, the female part of the Plug goes to the Ignition Switch. So you want to jumper the 2 of the female holes but you cannot tell the holes you need.

Pic 4 In this pic the Yellow Arrows point to the Holes that the Jumper Wires need to go into (bypassing the Neutral Safety Switch) .

If your Starter Motor Cranks you know your Neutral Safety Switch has issues.

If your Starter Does not crank this test still does not tell you if it is the Neutral Safety Switch or the Ignition Switch.

Next you want to see if the Neutral Safety Switch is making contact in Park or Neutral. You can use an Ohm Meter or a Test Light that has Batteries in it. You put the Shifter in Park and probe the 2 male connectors that have the Purple wires going to them. If your Neutral Safety Switch is making contact your Test Light will Light and/or your Ohm Meter will show that you have a connection.

If your Neutral Safety Switch is making Contact and jumper wires on the Connector did not allow the Starter to crank you likely have a Ignition Switch problem.

Unfortunately I found out that what appears to be an Ignition Switch issue can be an issue with what turns the Ignition Switch.
See the below thread if you are interested in that:
http://www.peachparts.com/shopforum/diesel-discussion/333785-steering-colum-lock-ignition-lock-housing-causes-ignition-switch-failure.html#post3089265

Does anyone know if the wrong wires are wired up, will that drain a battery ?

If you are speaking of the 240D converted to the Manual Transmission? And, it has the Same Connector if the 2 Purple (Violet) wires on the Female Electrical connector were connected together that would remove the Neutral Safety Switch from the Circuit and the Starter Solenoid sould be now be connected direct to the Ignition Switch.

Any, Electrical current going through that Circuit would be coming from the Ignition Switch.
The Manual Transmission Back up Light Switch would need to be wired to the front 2 Wires on the Female Connector but there Might already be a Connector that just plugs into it.

I can't see anything in the old NSS Circuit that would cause a Battery Drain except if the Ignition Swich was allowing some current to go though it.
If the Ignition Switch was allowing Current to get through whe you disconnect the Wire from the Smallest Terminal on the (it may also be Purple or Violet) Starter Solenoid and put one probe of the Digital Volt Meter (set on VDC) and another probe to ground you would show Voltage when there should be none.

Yes, it is a 240D. Not sure of the year, which is a sad commentary on me right now. I grabbed that 4 pin connector at the JY and I am going to solder a jumper in place instead of the wires under the car. I have no back up lights yet as I am looking for the 2 prong pigtail that goes to the shifter. The battery sat outside in some cold weather for 6 weeks and it fired up the car no problems this past weekend. The battery is new so I doubt the battery is the problem. Now, deader than a door nail. I also had a 6 plug connector under the dash and one pin fell out during the conversion. My clock doesnt work so I am thinking that pin had something to do with it. I think the wire was green. The real problem is that I am a total dummy when it comes to electrical stuff. After I melt and burn something a few times, then I will understand and get it. I got this weekend to tinker with it, however.

You can still figure out if it's your ignition switch if you take your test light and ground pin #3 on the block with the light and turning the ignition to see if it lights up. It doesn't, then it should be your ignition switch.


Edit: As Diesel911 pointed out, this test is made on the female block. Not the male plug with the pins.

Thanks I never looked at the Wiring Diagram.

Jumper Would this Work ?
 

Looking at the 4-prong plug, would this jumper work ? If so, this gets rid of wires under the transmission tunnel. I am still looking for the back up light plug which goes on the shifter. I need to find one of those at the JY. I assume the other 2 holes go for the back up light ? If so, then that would seem simple to run a wire to this plug as well.

BTW--although this might be old news, those metal prongs are actually very clever items. There is a hole that runs through them where one can run the wire and a dap of solder at the top.

This jumper would connect the violet wire with the violet wire with the white line.

Thanks !

I can't tell orientation by the picture, but if holes #3 and #4 are jumped, it will work. Hole #3 is ignition switch start position power and hole #4 is the starter solenoid kick on.
Hole #1 is switched power and #2 is reverse lights. You can harvest a wire connector for the shifter switch from a wire leading from the relay box on the driver side wheelwell to the firewall.


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Mybe this Pic will help, I numberd the holes/sockets.

The shifter has a 2 prong deal, which looks a lot smaller than the type pictured. I am assuming that if my jumper works, then the 2 remaining holes/prongs go for reverse lights. Right now, that is not hooked up. I am thinking that the 2 prong plug for the shifter is somewhat unique, only from a manual.

Right now, it is brutally cold outside ... at least by S.C. standards. :D I got about 1/16" layer of ice on the cars, so I am thinking no outside work on the cars until after noonish so it warms up a bit. The battery has been charging since yesterday 8 am-ish, so it should be good to go. I am thinking that the 6 prong plug that jumped a wire during re-assembly might have something to do with my electrical issues. I have no dome lights and no clock and they should be working.

The 2 prong connector is not unique actually. It is a standard Merecedes plug of that era. As I stated earlier, you can harvest that plug( and wire) between the firewall and relay box. See this pic, it's in this area that I marked "temperature wire connector" for another thread.

http://www.peachparts.com/shopforum/..._display08.jpg


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OK, I will grab one and size it up. I have a spare five speed shifter so I can tinker in the warmth of my kitchen to my wife's chagrin ... LOL.

Hello everyone, I know is a very old thread but hopefully someone can help me:
So couple of weeks ago my e300 92 turbo diesel started to not start directly in P. So I came up with this topic and by pass the neutral safety switch…and then was starting right away, but for sure in all gears…
Yesterday I manage to change the switch…take the by pass..and still the car starts in any gear…(I try to install the new switch in the “same” position as the old one…)
Please help, will like to have the safety switch working properly!

When the neutral safety switch is bypassed there still could be an issue with the shifter bushings. Both the exterior ones and the ones at the base of the shifter stick. On my 84 300D those plastic/nylon bushings are cheap but a bit of work to deal with.

On my 84 300D is a method of lining up the neutral safety switch with the smoot end of a drill rod. I don't know if that method is used on your vehicle, and I cannot recall it from memory. There may be some threads on replacing the neutral safety switch on your year and model and there is definably some on my year and model.
DIY links:
http://www.peachparts.com/shopforum/diy-links-parts-category/146034-fast-navigation-do-yourself-links.html

In post 9 you can see where a shifter bushing at the base of the shifter moved.
http://www.peachparts.com/shopforum/diesel-discussion/387917-shift-linkage-bushings.html

I have been on the forum since 2007 and I firmly believe the peoples repair struggles could be greatly eased if they bought the manuals for their vehicles. They save you much time, trouble and money.

You look in the manual and understand the way Mercedes wants it done and if there is some sort of special tool come back to the forum and see how people did it without the tool or made the tool.

I don't know if this is a match: https://www.youtube.com/watch?v=uP3ywEZj2jQ

See the attached picture. There is a hole in the transmission housing and see the red arrow on the neutral safety switch that points to an alignment hole.

The right sized drill but smooth end goes through that hole and into the hole in the transmission body and then the 2 hold down bolts are tightened. When those are tightened you remove the drill bit and the neutral safety switch should be adjusted.