From directions from Funola I have found the junction box for the wires from Key start switch to NSS. The box sits on the firewall just above the throttle pedal. It can be carefully preyed open with a flat tip screw driver.
Viewing from the rear is with a mirror. Ground a VOM and prob the violet
wire in the box working in the mirror. Very easy to do if you are a Dentist.
Meter showed only 1 volt when wife turned the key to start. New switch is on order.
WARNING: Do not mess with the wires with the cap removed.

Is there a way to get rid of the popup adds?

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1984 300SD turbo 126
"My true love"

God made me an atheist and who am I to question His wisdom

If you sign in, I do not think you should get pop up ads.

Thanks for the tip. Signed in no adds.
Does anyone know the head style on the three screws that hold the switch into the lock? Have to rig up blind driver of some sort.

__________________
1984 300SD turbo 126
"My true love"

God made me an atheist and who am I to question His wisdom

Which switch is on order? You also need to probe the VI/WH wire to determine which switch is needed.

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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

Gears and Funola,
Many thanks for posting the images of the plug and wiring diagram.

I need to go out and take another crack at this. I got stuck at the grocery tonight. Had to jump the screw terminal under the hood to get her started. At least I got home. My pushbutton starter didn't work.

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79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles

When I jump from the screw terminals at the firewall the car cranks strongly. I don't think the battery is weak. I'll have to get out there and run some more tests.

__________________
79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles

Hah, found C146! I was confused because it is behind a piece of panel carpeting up against the tunnel. Now I can probe the vi and vi/wt lines as I turn the key.

__________________
79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles

Yessss!!!

Ok, I poked through the insulation of Vi and vi/wt with pins and measured the voltages with respect to ground.

On vi/wt I get 0v with the key off then 11.26v with the key on start.

On vi I get 0v with the key on and o.127v with the key on start.

Looks like there is a problem at the NSS.

Btw there is still the can of worms about the solenoid drawing a lot of current. I bet if I unhooked the solenoid at the screw terminals in the engine compartment the vi wire would jump up. It looks like it is getting pulled down by a big current load. But then again that could be a bad contact at the NSS adding too much resistance. Either in the connector or internally in the NSS.

We will find out soon.

__________________
79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles

Picked the new start switch, opened the box, placed a screw driver in the slot, Guess what, no spring back. That part was left out. No wonder I got a real good price. So much for a made in India switch.
I will go for a MB switch.

This has been a great experience. I have learned so much from all the posts from you guys. Thanks

__________________
1984 300SD turbo 126
"My true love"

God made me an atheist and who am I to question His wisdom

Yeah, I wish I had bought an OEM NSS instead of this half price special I have in the car. Some of these cheap parts cause a lot more problems than what they save in money.

I jumped my solenoid again to get home. Had to do it yesterday too. No longer intermittent. It's broken all the time now. At least I can get it started with a wire.

Looking forward to getting my NSS in the mail.

__________________
79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles

I jumpered the terminal block with a digital ammeter and the solenoid drew 8 A when cranking.

__________________
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

Before condemning the switch, verify that the spring-back is in the switch and not in the lock mechanism. I said it's in the switch but I am not 100% sure about that.

__________________
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

Hi Funola
I have watched several videos from Kent Bergsma at mercedesource and he enplanes that the spring back is in the switch not in the Key lock assy.
That when the spring back is gone that is a sign the start contacts have disinterested from years of arching. I hope he is correct so I don't have to to to my local parts guy and eat crow.

On another topic that you may know about. Regarding the HVAC amplifier that works withe the Push Button heater unit. Does it ever go bad or is it always the front end button unit?

Opps I think I just hi-jacked my own post.

__________________
1984 300SD turbo 126
"My true love"

God made me an atheist and who am I to question His wisdom

Thanks! Good data. I'll go down and check mine. I was afraid I'd blow my meter's fuse up with this test. Um maybe I will if I'm drawing too much.

Well, time to make some smoke!

Edit- ok tried it. Bounced around between 6.5 and 8A. Thanks again.

__________________
79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles

Ok, got my new Mercedes Benz neutral safety switch in and the car starts fine now.

I believe that was it. The old one Looked good and didn't sound rough when I flicked it. I think the contact resistance was too low inside. Plugging and replugging the connector didn't help a few days back so I am pretty convinced the NSS was bad.

Thanks again to this great forum.

__________________
79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles