When I turn the ignition switch I get nothing.
Trying to narrow down the problem.

Throwing this out cause I don't have time now to
read through all the threads I see.

I have a good used starter in the garage.

Thanks,
Jeff

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1984 300SD 300,000 miles--two tank WVO setup
2.88 diff & 500SEL anti-squat rear end

I think you've already got it pretty well narrowed down - NSS, starter or ignition switch is about all it could be. If it were me I'd do the NSS and ignition switch first as the starter is a pain to get to.

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Current Stable

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Try to move the gear shift lever around to see what happens. If it cranks that means your neutral safety switch could be faulty or out of adjustment. On the starter I would jump the starter solenoid to see if the starter cranks. If jumping the solenoid produces no result then you have narrowed the problem down to the starter or the starter solenoid. If the key turns to the crank position more than likely your ignition switch and tumbler are OK. I presume you have already checked your battery and battery cables especially the ground cable.

Or the one thing you didn't mention.....the ground straps

I changed out 2 starters before finding a loose eng-chassis ground strap.

BTW, the starter isn't as difficult on the W126, compared to the W123.

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Sam

84 300SD 350K+ miles ( Blue Belle )

Thanks everyone,
OK--jumping the starter on the SD--
jump between 1st & 3rd terminals in the junction box
on passenger side fender? With key in on position? trying to crank?

New battery this year--recleaned terminals.
Put in a rebuilt Bosch starter maybe four years ago.

Thanks,
Jeff

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1984 300SD 300,000 miles--two tank WVO setup
2.88 diff & 500SEL anti-squat rear end

if MB carried the same design over to later years, there is a 4 pole wiring junction next to the knee panel, its a 4 wire junction with two thick and two thin wires, one of the thick is from the key and the other comes back from the NSS contact, the thins are for reverse lamp.

if you bridge the 2 thick wires - you can bypass the NSS and test if the key starts the engine, if not then test at the 3 pole junction in the engine room. If you cannot energize the starter there, your starter is not getting a complete circuit to rotate the motor.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

Could also be shift bushings. If they're bad or missing entirely, as can happen, you may not be in the gear you think you're in. I know with Park in particular it can be in enough to take it out of drive and engage the pawl but not enough to disengage the NSS.

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1979 300D 040 Black on Black - 1985 300D Maaco job (sadly sprayed over 199 Black Pearl Metallic) on Palamino

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If the meaning of "nothing" includes no crank or even a solenoid click AND you know that the battery is charged and the battery cables and grounds are clean & tight:

You have to go through the tests. Key to "start" sends current to the small wire on the solenoid on all vehicles of this era. Test this. You should also have full battery voltage at the cable at the starter.

There is also a junction block under the hood on the passenger side that can be used to bypass some of the switches. I forgot exactly which ones. This is where I connect a switch to bump the engine when don't want to turn it with a socket or use the ignition key. It is also in the FSM.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

Confirmed by jumping terminals 1& 3 in junction box on pass fender.
Only got a click with the starter in the car.

Hooked up the good used starter on garage floor to the battery
and connecting the solenoid wire to terminal #1.

After jumping 1 & 3 solenoid engages and motor spins.

Looks like another Friday night under the car.
This after finishing redoing the entire rear end last week.
It never ends...........

Thanks to all for the help.
Jeff

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1984 300SD 300,000 miles--two tank WVO setup
2.88 diff & 500SEL anti-squat rear end

Keep your old starter. it could be as simple as contacts. You really need to know how much charge the battery has.

A click is the solenoid contacts closing and not enough current flowing to turn the engine. What if you have a bad connection, swap starters, cause the new starter to have a good connection and throw your old one away - or worse, trade it as a core for the crappy remans commonly available?

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

Just finished putting in the spare starter.
Fired right up. Cleaned up the ground strap which wasn't bad.
Not terrible on the 126--pull the aircleaner--drop the exhaust.
I had done this before so the big hex bolts broke loose fine.
My wife has small hands and she helped out starting some of
the hard to reach bolts.

There is an alternator shop here in town that does good work.
It is a one man shop and I think he might rebuild starters, too.
I will give him a call to see if he can work on them.

The Bosch reman I put in was practically new, so I should be good for a while.

Thanks again everyone,
Jeff

__________________
1984 300SD 300,000 miles--two tank WVO setup
2.88 diff & 500SEL anti-squat rear end

On a side note, met a fellow member when I was starter stranded in the
local Post Office parking lot before getting towed home.
His name is Tom and he goes by 5cylinder.
Saw me with my hood up and came over to try and
figure out the problem. Great guy. He correctly guessed the starter.

He drives the best looking 85 300CD I have ever seen.
Immaculate inside and out. Super clean engine bay.
Original paint is black & looks new. Should have taken some pictures.

Anyway, it was nice to have a fellow traveler come over & help
out a total stranger.

Jeff

__________________
1984 300SD 300,000 miles--two tank WVO setup
2.88 diff & 500SEL anti-squat rear end

X2 on keeping the old starter. References Stretch's wonderful thread on rebuilding a 617 starter (something along the lines of "a 617 starter isn't just for Christmas") and keep it as a spare. I used his thread as a guide to refresh my 601 starter when I had the car taken apart for a clutch and an oil leak.

I've offered assistance to other Benz drivers in the past. The most recent was a gasoline W126 hood up at the gas station. I asked if he was having trouble and he said it died and wouldn't restart. The bad thing was, he told me he had a mechanic on the way and the mechanic thought it was the injectors. At that point, I just wished him luck and walked away. I wasn't about to sit there and explain Jetronic to him and suggest a new mechanic. Oh well. I've also had multiple people come to the auto garage I worked at specifically asking for me by name because word got out I was in the business of fixing our old cars. I left everyone with a paper with info so they had the site and my username. It's nice to induct new members.