OK just went through this and some of the instructions I found were wrong. So here is the latest. If you've made sure that your battery has enough cold crank amps left to power the starter, and you've used a remote starter switch to make sure that the car will run with the key on and then the starter engaged via remote starter (see my post about Remote Starting a W124) , you likely have a problem with the Neutral Safety Switch (NSS).

1. If you can do this while it's on a lift, you'll cut the time by at least half and 10X less swear words.

2. It's tight in there between the side of the tranny and the trans tunnel so you'll have to position yourself so the you are facing it and can use both hands palms facing away from you.

3. Use multiple light sources to see what you are doing.

4. You have to rotate the white locking ring CLOCKWISE to be able to gently pry up the electrical plug away from the Neutral Safety Swtich (NSS).

5. Cut the plastic cable tie on the speedo cable that is mounted on a bracket in front of you to get more room.

6. Release the shift lever on the side of the NSS by removing the bolt with 10mm ends that clamps the lever onto the shift rod spindle, spreading the gap with a twist from screw driver and then gently pry the metal lever up and away.

7. This is the 2nd hardest part- to remove the 10mm bolt at the 1 o'clock position that holds the NSS in place (it's hard to see, use the new replacement part as a guide),you'll first have to guide a small 1/4 ratchet with a 10mm socket to the bolt head using only the tips of you fingers on both hands. Once you've loosened the bolt, unwind the bolt by giggling it with the finger tips of both hands until it comes all the way off.

8. Now you can loosen the bolt at the 9 o'clock position. Make sure to notice that the metal shift lever has a hole in the middle of it half way up where a tab from the plastic NSS lever fits into. My plastic lever just broke off as I was withdrawing it. I believe that the reason why my NSS was failing because the plastic lever had cracked and would only properly align itself intermittently allowing for a start in Park or Neutral.

9. Before you re-install the NSS, use a wire brush to clean off the trans gear shaft spindle head, as well as the shift lever socket itself. Also spray some contact cleaner on the NSS plug. Also, put a small film of grease on the threads of the bolts for the NSS. This will make it easier for the bolt to seat itself in the threaded spots.

[COLOR=black][FONT=Verdana]10. To install the new NSS, insert the NSS and place it so that the bolt at the 9 o’clock can be partially threaded in. This is the HARDEST PART… using only your finger tips (no room to work a whole hand in the space), feel around to find the spot where the bolt fits into the eye of the NSS. With both palms facing toward the trans pan, work the bolt into the eye with your finger tips. It’s not easy at all. The bolt has to go in dead center for it to be able to be threaded in. Remember you can move both the bolt within the eye, as well as, the eye itself until you can find the spot for the bolt. You’ll know you’re in when the bolt rotates in with a slight resistance and doesn’t wobble. Only when you are sure you have the bolt threaded properly will you then use a socket wrench to tighten the bolt down but not all the way.

11. Now re-attach the shift lever while making sure that the tab on the black plastic lever of the NSS is properly situated in the hole of the shift lever.

12. Move the shifter into Neutral gear, slide the NSS as far left as it can go. Now tighten the two holding bolts until snug (not Herculean snug). Next, with the white locking collar in the unlocked position (rotated clockwise and away from you until it stops, a rotation distance of about ½ inch, plug in the NSS cable. It’s a snug fit with no slop. Now rotate the white ring in the opposite direction to lock the plug into place. If it will not easily rotate, it usually means that the plug in not plugged in all the way down and needs to be pressed further inward to allow for the channels of the locking ring to slide past the tabs at the sides of the NSS plug.

13. Start the car in Neutral. Turn the car off. Shift to Park and start the car. If it starts in both gears, the NSS is in the position it needs to be in.

Lastly, using a plastic cable tie, re-attach both the speedo cable and the NSS cable to the bracket at the side of the trans pan.

You should be good to go!

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03 CLK430 Cabrio 211K Pweter Silver/ Oyster Leather
90 300SEL 214k Pearl Black/ Alto Grey/Black Leather

Prior: 85 190E, 88 300TE, 89 300TE, 90 300E 2.6, 90 300TE, 92 300E 2.6, 91 and 93 300SL, 87 Ferrari Mondial Cabrio

What a pain in the buttocks - especially for those of us without a lift. Think it is the same for a 126? I have a 1981 300SD and am having no start no sound problems which makes me think it is not the starter solenoid. For a while it would come back and start fine for months on end. Now nothing.

Serves me right. Let wife drive it for a whole day.

If you can't start in Park or Neutral, then it's likely to be the Neutral Safety Switch. Could the starter be stuck? Just in case, the ignition key needs to be turned of then on again, after shifting into neutral gear, to re-engage the starter.

Good luck.

__________________
03 CLK430 Cabrio 211K Pweter Silver/ Oyster Leather
90 300SEL 214k Pearl Black/ Alto Grey/Black Leather

Prior: 85 190E, 88 300TE, 89 300TE, 90 300E 2.6, 90 300TE, 92 300E 2.6, 91 and 93 300SL, 87 Ferrari Mondial Cabrio

Yes, I have tried everything. Did not know that it could start in Neutral. Have tried that too just in case.

I updated my post above with and additional tip on how to make sure the NSS is in its proper position for it to function properly. Basically, it needs to be slid over to the left while in Neutral gear, bolted down and then tested in both Park and Neutral gears.

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03 CLK430 Cabrio 211K Pweter Silver/ Oyster Leather
90 300SEL 214k Pearl Black/ Alto Grey/Black Leather

Prior: 85 190E, 88 300TE, 89 300TE, 90 300E 2.6, 90 300TE, 92 300E 2.6, 91 and 93 300SL, 87 Ferrari Mondial Cabrio

Wow!

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I have never met a man so ignorant that I couldn't learn something from him. -Galileo Galilei, physicist and astronomer (1564-1642)

Reverse lights are a better indicator of the correct position than starting in N and P.

There is a 4mm hole in the arm on the switch and in the switch body. This allows you to insert a small dowell to line them up. I forget what position it lines up but I think it's N.

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90 300TE 4-M
Turbo 103, T3/T04E 50 trim
T04B cover .60 AR
Stage 3 turbine .63 AR
A2W I/C, 40 LB/HR
MS2E, 60-2 Direct Coil Control
3" Exh, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
Vented Rear Discs, .034 Booster.
3.07 diffs 1st Gear Start

90 300CE 104.980
Milled & ported head, 10.3:1 compression
197° intake cam w/20° advancer
Tuned CIS ECU
4° ignition advance
PCS TCM2000, built 722.6
600W networked suction fan
Sportline sway bars
V8 rear subframe, Quaife ATB 3.06 diff

Sounds what I did for the NSS on my 300SD as I had no reverse lamps. Just left shifter in reverse (car up in the air fully) and fiddled with the switch until the reverse lamps illuminated.

Tightened it down and verified the shifter moved from P to 2 with no binding.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

You left out the most important thing:

Make sure the replacement NSS is an original MB part, or you will be doing this job more than once within a very short time span.

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2008 E350 4matic / Black/Anthracite

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Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black

I haven't had any luck finding neutral safety switch replacement instructions on a w123 300d. How similar are these instructions?

I took a quick look under the transmission and it seems like the same story. Very little room to work with.

How functional is this current plastic cap? If it's rubbish what is the part called and where can I order one?

P/N: 115 992 03 10 - Bushing
You have a little life left in it.

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1986 300E (3/2002) Rear ended and totaled (10/2009)
2000 Xterra (5/2000)
1992 400E (11/2009) -Sold
1986 300E (12/2009) - Sold
2004 E500 Wagon (6/2013) - Sold

Fixed it! Wow you were right that bushing was toast. Had to make my own little press to force the new one in. It looks like the switch and the bushing were the problems, now my car starts without fail!

Thanks for the guide.

For my 1990 300E, the NSS alignment hole is right next to and just below the middle rivet. The tranny needs to be in Neutral for everything to line up.

Just remove the electrical plug to gain access to the upper bolt. Loosen the two bolts holding the NSS. Partially, insert the right size Allen wrench (test fit while the NSS is still on you bench. With the trans shift lever in front of in Neutral or Park (depending on your car), slide the NSS and wiggle the wrench until the Allen wrench finds the hole in the NSS and everything lines up with trans lever. Tighten the bolts and reconnect the plug. Start the car and test starting in both Park and Neutral. Done!

Of course all this is in the factory shop manuals... but here's some of my pictures and info from an expert in the matter:

"The reason Benz wants the NSS aligned with the factory bore hole (in the NSS body) and the lever is b/c they want the NSS in N or P (depending on your car) when the transmission detent actuator INSIDE the tranny is at the correct position.

This allows alignment of the NSS to the transmission..NOT the gearshift .
The gear shift lever and linkage is then adjusted so as to line up with the shift gate. Alignment using the shiftgate or back lamps as the base is completely incorrect, as that can lead to the NSS not being aligned correctly with trans gears.

NSS aligns to trans mechanics , and then the ghearshift aligns to the shiftgate.

Using the shiftgate as the alinment will often get the results , but it is not correct and can lead to a short lived NSS."

Attached Thumbnails

       

__________________
03 CLK430 Cabrio 211K Pweter Silver/ Oyster Leather
90 300SEL 214k Pearl Black/ Alto Grey/Black Leather

Prior: 85 190E, 88 300TE, 89 300TE, 90 300E 2.6, 90 300TE, 92 300E 2.6, 91 and 93 300SL, 87 Ferrari Mondial Cabrio

Well replacing the switch only partially fixed my intermittent starting. I replaced the ignition switch as well so it looks like the starter solenoid is next..