Neutral Safety Switch Wiring Question - PeachParts Mercedes-Benz Forum

StaggerLee · #1 07-08-2011, 12:32 AM

1980 300TD non-turbo chassis - 1981 Turbo motor and trans swap project.

There are 4 wires in the neutral safety switch plug on the turbo transmission. I can match up 2 of the 4 with the wires from the non-turbo transmission; the kick down switch and the back up lights.

The two I'm not sure how to proceed on are the Violet/white and solid Violet from the 1981 NSS and the Brown/Yellow and Brown Ground from the Chassis.

On the 1980 wiring diagram, the violet/white comes from the ignition switch and goes to the A/C starter relay. Then a Brown/yellow goes from the A/C starter relay to the NSS and a brown ground wire comes out. The violet wire that powers the pre-glow and starter also comes out of the A/C starter relay.

On the 1981 wiring diagram the A/C starter relay is bypassed. The violet/white comes from the ignition switch and goes straight to the NSS. The Violet wire going to the starter and pre-glow system comes out where the brown ground comes out in the 1980 diagram.

Any suggestions? I'll try to post the diagrams if that helps.

Thanks!

Jeremy5848 · #2 07-08-2011, 02:33 AM

The violet and violet/white pair in the 1981 transmission are from the starter lockout switch (the "Neutral safety switch," which really should be the "Neutral or Park safety switch"). I don't know what the A/C starter relay is -- something that turns off the air conditioning while the car is being started, maybe? If that relay is bypassed in the 1981 diagram, there must be something else to do its function. If the only 1981 parts are the motor and transmission then you probably will want to wire following the 1980 diagram. Please post the diagrams; I'm not as familiar with those models as I'd like to be.

Jeremy

StaggerLee · #3 07-08-2011, 11:02 AM

Working on the diagrams now. Should be uploaded soon.

StaggerLee · #4 07-08-2011, 11:30 AM

All of the wires for the NSS on the 1980 chassis are a small gauge as if they are used to trigger relays. The wires coming out of the NSS Plug for the turbo trans have two small gauge for the back up lights and kick down switch but the violet and violet/white are a much bigger gauge.

I've removed the A/C all together if that makes a difference with the wiring solution.

The first pic is the 1980 Diagram

Stretch · #5 07-08-2011, 12:17 PM

Hey StaggerLee I haven't got the answer but do you want some pictures of my '81 euro? I can make 'em tomorrow for you. (I've been given time off for good behaviour so I'm working on the car)

Jeremy5848 · #6 07-08-2011, 12:27 PM

Quote:

Originally Posted by StaggerLee

All of the wires for the NSS on the 1980 chassis are a small gauge as if they are used to trigger relays. The wires coming out of the NSS Plug for the turbo trans have two small gauge for the back up lights and kick down switch but the violet and violet/white are a much bigger gauge.

I've removed the A/C all together if that makes a difference with the wiring solution.

The first pic is the 1980 Diagram

The 'violent' wires in the 1981 circuit are larger gauge because they have to handle the current of the starter solenoid (the "Bendix" as it's sometimes called) all by itself. The 1980 circuit 'cheats' and uses a relay so the brown wires can be lighter gauge.

If you still have the A/C-starter relay in the 1980 chassis, all you have to do is to connect the brown/yellow wire from the relay to the violet/white wire from the NSS. Next, connect the violet wire from the NSS to the brown ground wire. Ignore the difference in gauges.

The car should now start normally. If you have thrown away the A/C-starter relay we can work around that -- let me know.

Jeremy

StaggerLee · #7 07-08-2011, 12:43 PM

Thank you Jeremy5848!
I had a hunch that is what I needed to do but had no idea if I was right or not.

I'll get to work on it and report back. I can't be the only one doing this swap and maybe it will help someone else.

Yak · #8 07-08-2011, 06:27 PM

Here’s what happens:

On the ’80, the skinny Vi/Wh gets +12v in START. That +12v travels to pin 86 on the relay. The relay will switchover from pin 87a (providing high amp power to fuse 5 <> and the A/C and others in RUN) to pin 87 and the fat Vi wire (providing high current to the starter solenoid) ONLY if there’s a path to ground on pin 85. Pin 85 is the Br/Ye wire from the relay to the NSS. It gets a path to ground only in P or N via the Br wire that goes from the NSS to the chassis.

On the ’81 the fat Vi/Wh gets +12 in START, travels to the NSS and gets a path to the starter solenoid via the fat Vi in P or N.

To use the ’81 NSS/tranny switch in the ’80 harness you should be able to connect the skinny Br/Ye from the car to pin 3 (#50) on the NSS, and the skinny Br from the car to pin 4 (#50) on the NSS. As you’ve already figured out, pin 1 is the kickdown (Bl/Ye/Re) and pin 2 is the reverse light (Gr/Ye).

The advice to connect up the car’s Br/Ye to the NSS Vi/Wh and the car’s Vi to the NSS Br probably won’t work since it refers to a mini-harness going from a 4 pin connector (C146) in the ’81 near the gas pedal on down to the 4 pin connector on the NSS. The ’80 may not have that harness, so your wiring really should be plug-n-play.

I hope you haven’t pulled the starter/A-C relay since, at least per the diagram, if you did you won’t get power to the <> A-C controls.

StaggerLee · #9 07-09-2011, 01:01 PM

Yak - The AC starter relay is in tact.

It seems like you're telling me the same thing Jeremy5848 said:
"the skinny Br/Ye from the car to pin 3 (#50) on the NSS"... Pin 3 (#50) on the NSS is the thick VI/Wh.

"and the skinny Br from the car to pin 4 (#50) on the NSS"... Pin 4 (#50) is the thick Violet wire.

"The advice to connect up the car’s Br/Ye to the NSS Vi/Wh and the car’s Vi to the NSS Br probably won’t work" except it seems like that is what you're recommending I do.

I'm going to try it and see what happens. Should have a thumb's up/thumbs down today or tomorrow.

StaggerLee · #10 07-09-2011, 01:07 PM

"The 'violent' wires in the 1981 circuit"

Watch out for those Violent wires. Nobody likes violence.

Thanks again Jeremy!

Yak · #11 07-09-2011, 07:46 PM

Quote:

Originally Posted by StaggerLee

Yak - The AC starter relay is in tact.

It seems like you're telling me the same thing Jeremy5848 said:
"the skinny Br/Ye from the car to pin 3 (#50) on the NSS"... Pin 3 (#50) on the NSS is the thick VI/Wh.

"and the skinny Br from the car to pin 4 (#50) on the NSS"... Pin 4 (#50) is the thick Violet wire.

"The advice to connect up the car’s Br/Ye to the NSS Vi/Wh and the car’s Vi to the NSS Br probably won’t work" except it seems like that is what you're recommending I do.

I'm going to try it and see what happens. Should have a thumb's up/thumbs down today or tomorrow.

Maybe a nuance difference, but yes, functionally the same. "connect the brown/yellow wire from the relay to the violet/white wire" vs. "connect the skinny Br/Ye from the car to pin 3 (#50) on the NSS"

I'm assuming when you get the '81 tranny and see the NSS that there won't be any wires there, just 4 pins, so there wouldn't be a vi/wh wire. Identifying it by pin number on the NSS may mitigate a "which pin is which on the '81"

Depending on which source you use for diagrams it may look like there's a pigtail and 4-pin connector on the '81, but that connector that is right next to the tranny in the diagram is supposed to be up in the footwell/console area. That's what I meant by "mini-harness". Compare 36 and a little to the left in 81 NSS to 38 and 43 in the 80 NSS file.

Wire colors are in german on the pdfs. Sw - schwartz = black, ge = gelb = yellow, etc.

StaggerLee · #12 07-14-2011, 02:45 PM

I neglected to mention that I kept the connector and 8" of pigtail when I got the NSS so there wouldn't be any question about pin #s.

I connected it up as stated and it worked fine. I DID, however, lose power to my windows and no, I didn't do anything to my A/C Starter Relay. I'll have to look in to that a little further because I lost the blinkers too. (Fuses were the first thing I checked).

So, the car is almost road ready and we hope to have it at NWGTG.

StaggerLee · #13 07-14-2011, 05:40 PM

Hey Yak - I couldn't find the reference on the diagram to the window power wire. Can you help me with that? My FSM says that the 1980 window relay is behind the gauge cluster.

Thanks for your help.

Yak · #14 07-14-2011, 10:56 PM

The window relay is supposed to be behind the instrument cluster. It's #11 in the diagram. But before you pull the cluster to check, here's more stuff you can check in the fusebox with a meter.

I jumped one trace over and the starter relay doesn't send power to fuse C, it sends it to fuse 5. I'll edit post 8 to correct that.

Does the glove box light work? That light is on the same path as the window relay closing circuit - if the light works, then the relay should at least be getting the signal to close (it may/may not also be getting power and may/may not actually close). This basically checks fuse #4 and the ignition switch. Fuse 4 sends power to the window relay pin 86. The relay sees +12v on pin 86 and closes from 87a to 87.

Then check both sides of fuse 2. The window relay gets power from the "upstream" side of fuse 2 - which gets power from the battery via the light switch. If there's power at fuse 2, then pin 30 at the relay should get power. If fuse 4 is good with power and fuse 2 is good with power, then the window relay should move from 87a to 87 and send power to fuses A and B. You can put a meter on A and B and see if they get power in position II.

If you've got power from fuses 2 and 4 but no power at A or B, then the window relay isn't closing when it should and you could pull the cluster and replace or check that.

If the blinkers and the windows are only a few components amongst many, then I'd suspect a problem with the ignition switch supplying power to circuit 15 or maybe 15R. 15R gets +12 from the ignition switch in I, II and START and goes to fuses 4 and 6, you can check them with a meter; 15 gets +12 in II and START and goes to fuses 8 thru 14 and D. You already know 15 gets power in START, because that's where the power for 30 on the starter relay comes from. You just need to verify it also gets power in II.

StaggerLee · #15 07-15-2011, 10:32 AM

Thanks for the help Yak! I think I've got it.

I checked power at all the fuses and was getting intermittent power at the window switch. I pulled the cluster and cleaned up the relay contacts. Viola! Window power. I also changed switches to one with less OPC in it. (Other People's Coffee)

So, I don't think the window power issue had anything to do with our NSS wiring of the 1980 chassis and 1981 trans. The description above works great.

I do recommend grabbing the NSS plug with 6" of wire to mate with the earlier wiring harness.

The blinkers were also a matter of cleaning contacts and changing a bulb.

Thanks again!