I have a 1982 300SD. Odometer stopped at around 270K. All glow plugs are new/working, new battery, new fuses, clean fuse box, new shift lever and trans lever bushings.

After replacing the neutral safety switch yesterday (genuine Mercedes NSS) my car will not start in P or N. I don't think that I have parking lights.

I have gotten the car started (I had been starting the vehicle by using a length of copper wire, bridging two wire terminals in a black box located on the passenger side, above the wheel well) and after turning off the engine, I was able to restart the car, once, using the key (in both P and N) but only once. I couldn't restart using the key after that.

After I first installed the new NSS, and couldn't get the car to start, I used the copper wire to start the vehicle and there was a sound that I hadn't heard before, and haven't heard after when using this method. It was kind of a quick, scraping sound. It almost reminded me of when I have sat in a gas car (quiet engine) and turned the key, not realizing that the car was already on, and it makes an unpleasant sound.

I installed the NSS exactly as it came out - white plastic collar rotated up, pulled out the wire plug, unbolted the NSS. New NSS in, wire plug in, white collar rotated down.

I did this on the streets of Queens, NY. I use the vehicle regularly, it's not garaged.

Does anyone have any idea of what the problem may be?

Did you get the index tab (plastic) of the new NSS in the guide slot of the steel selector lever on the side of the transmission? Did you insert a 4mm drill bit in the hole of the tab and rotate and bolt the NSS to that point on the transmission? (this aligns the body of the NSS to the arm of the selector)

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80 300SD (129k mi) 82 240D stick (193k mi)77 240D auto - stick to be (153k mi) 85 380SL (145k mi) 89 BMW 535i 82 Diesel Rabbit Pickup (374k mi) 91 Jetta IDI Diesel (155k mi) 81 VW Rabbit Convertible Diesel 70 Triumph Spitfire Mk III (63kmi)66 Triumph TR4a IRS (90k mi)67 Ford F-100 (??)

RS - yes, I did get the tab into the guide slot of the steel selector lever. I had someone shift the gears to make sure the plastic piece followed the selector. I didn't bolt it into place, I hadn't heard of doing that. I'm assuming thats a way to make sure that the plastic tab doesn't come out. 4mm drill bit, and maybe a 3mm nut & bolt? Let me know how to do that, if it helps.

No, there are two 10mm bolts that hold the body of the NSS to the transmission that go through slotted holes in the body of the NSS. There is a hole in the top of the lever of the NSS and a corresponding hole in the body of the NSS. You are supposed to fasten the NSS loosely on the tranny, then insert the drill bit through the two holes noted above and tighten the bolts. That should index the switch to the transmission. The lever on the NSS should stick into the metal selector without any fasteners, if you haven't bent or mislocated either one.

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80 300SD (129k mi) 82 240D stick (193k mi)77 240D auto - stick to be (153k mi) 85 380SL (145k mi) 89 BMW 535i 82 Diesel Rabbit Pickup (374k mi) 91 Jetta IDI Diesel (155k mi) 81 VW Rabbit Convertible Diesel 70 Triumph Spitfire Mk III (63kmi)66 Triumph TR4a IRS (90k mi)67 Ford F-100 (??)

There are instructions on here somewhere on how to jump the neutral safety wiring under the driver's side dash. Purple wires as I recall and something about pulling a connector apart and jumping the terminals. I would try that. It could be that your NSS was not the problem to begin with. There are a lot of documented cases on here of high resistance in the ignition start circuit causing your symptoms. If jumping the NSS circuit does not solve your problem, the issue is elsewhere. The fact that your starter made an odd sound--bendix sticking in the flywheel?--is an indication that the problem could have been in the starter all along and increased voltage caused by jumping at the terminals was overcoming the underlying problem.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

RS- I did it a bit differently than you explained. The way that I installed the NSS was to tighten the 10mm bolts to the side of the tranny, and then line up the tab into the hole of the metal shift lever, which was difficult, then to tighten down the shift lever. Your suggestion would have been easier. After I short-circuit start the engine, using a wire, and then turn the car off, I can start in P & N, only once, but it works the one time. Would that be possible, if I had somehow not indexed the tab to the hole correctly?

Kerry, I'm interested in where you're going, that it may be the starter. To give a broader picture, prior to installing the new NSS, I had a case of two missing bushings at the shift lever and at the transmission lever. I wasn't always getting the car into Park, and eventually, Neutral was hard as well, so I was starting, after a bunch of tries, in both. After replacing the bushings (I broke the NSS in the process, so I had to replace it) I hot wire started my car. Now that the NSS is in, and the bushings are in, I'm getting no start with the key EXCEPT when I've been driving, or had the car on. In this case it's a one shot deal, and then I can't get it key started again. Does this change the picture or give more clues?

You are pointing me back to the way you installed the NSS.

I said:


You said:

You probably have the NSS "twisted" one way or the other on the side of the tranny. If you did not insert a rod through the 2 holes, you do not have the contacts in the switch in place at N or P when the contacts on the arm are there to complete the circuit. You can try mislocating the shifter from the N slightly and see if it starts

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80 300SD (129k mi) 82 240D stick (193k mi)77 240D auto - stick to be (153k mi) 85 380SL (145k mi) 89 BMW 535i 82 Diesel Rabbit Pickup (374k mi) 91 Jetta IDI Diesel (155k mi) 81 VW Rabbit Convertible Diesel 70 Triumph Spitfire Mk III (63kmi)66 Triumph TR4a IRS (90k mi)67 Ford F-100 (??)

I do not know if your cars wiring is the same but I got part of this quote from another Forum concerning a no cranking problem with an 84 300D.

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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84 300D, 82 Volvo 244Gl Diesel

RS- that is a great idea, I'll try that first!!!

Diesel- thanks! I just put in a brand new, Mercedes NSS, but, it could be faulty. It's possible that I've installed it incorrectly, which is going to be my first easy test. After that, I'll try your suggestion. I'm also hearing that I may have a failing starter.

The thing that is unexplainable is that currently, I've been able to key start the car in park after driving it around some (I'd been bridging wiring in a box above the wheel well to get the engine to crank) If I can key start it at all in park, doesn't logic say that I have a working NSS? Or is it possible to start in park, after driving around a bit and shutting down, even without a working NSS? Please advise if you know...

thank you!!

I can't really explain this with an NSS issue, unless the contacts are so close to being "right on" that the thermal expansion is enough to bridge them when hot.

I am trying to figure out what caused you to change the NNS in the first place. Was it that the car started normally, then you lost a bushing, then you screwed up the old NSS, then you replaced it? Or what?

How was the car behaving before all this "drama"?

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80 300SD (129k mi) 82 240D stick (193k mi)77 240D auto - stick to be (153k mi) 85 380SL (145k mi) 89 BMW 535i 82 Diesel Rabbit Pickup (374k mi) 91 Jetta IDI Diesel (155k mi) 81 VW Rabbit Convertible Diesel 70 Triumph Spitfire Mk III (63kmi)66 Triumph TR4a IRS (90k mi)67 Ford F-100 (??)

Perhaps there is a bad connection at the starter and running the car moves it around enough to get it to work and sitting causes the connection to deteriorate. Not very likely but it's all I can think of.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Since it is part of a system there could be one or more problems in any part of the system. Battery, Ignition Switch, Neutral Safety Switch, Starter Solenoid, Starter Motor and the Ground.

Outside of the above system is the Shifter Bushings that if worn might not allow the Neutral Safety Switch to work.

If you are able to access the Wires above the Pedal and jump them to bypass the Neutral Safety Switch and are able to safely drive around like that remembering to start only in Park you will be able to see if a problem with the Neutral Safety Switch/Shifter Bushings or not.

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84 300D, 82 Volvo 244Gl Diesel

I am having a similar problem but since I can always get the car started by jumping the wheel well terminial block I have not fixed it yet because I'm a procrastinator.

Since your NSS is new, it is not likely bad out of the box. It could be NSS alignment, high resistance in the ign elec switch (power comes in at pin 30, comes out at pin 15, high resistance/ bad connections in the circuit path from the battery to the starter. The path is:

Battery, starter motor big terminal, light switch pin 30, ign switch pin 30, ign switch pin 15, NSS pin 3, NSS pin 4, terminal block violet wire, starter motor solenoid (small terminal).

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked