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1984 300SD, 1994 S350
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46 Posts
Discussion Starter #1
I want to replace the electrical ignition block on the back side of the ignition for my 84 300SD. I pulled the cluster and looked inside the dash. It looked like the electrical block is screwed in from the back side or toward the front of the car. This makes getting the right tool in there impossible. I think I need to remove the whole ignition just to replace that electrical block, but how do I get it off ?
 

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Two '87 570SECs, one '87 560SEL
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4,443 Posts
Since diesels don't really have an ignition system, I'm confused on what you're after. Is this the ignition switch on the steering column?
 

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1984 300SD, 1994 S350
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46 Posts
Discussion Starter #3
Guess I should clarify, yes, it's the ignition switch on the steering column I'm talking about. On the backside, there is a large switch block that is held on with screws, the screw heads are facing the front of the car. So, I need to remove the whole ignition switch just to change out the block on the backside. What is the procedure for ignition switch removal ?
 

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1981 300 SD, 1994 C280, 1990 560 SEC
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618 Posts
I believe you are going to have to remove the ignition assembly to get to the ignition switch on the back. If the ignition isn't broken once you have it out you can turn the key and the piece that holds on the switch plug will turn so that it can pull off. It is designed so that you can't get it off so that you can't hot wire it. Inside my ignition broke and I ended up tearing up the plug that goes into the switch. Had to buy new plastic piece and put the plug back together. The plug has to come out to get at the switch part off of the ignition. You may be able to get the plug off if the key and ignition still work without removing the ignition though I doubt the switch will come off after that without removing the whole ignition assembly. It turned out that my switch was fine but the ignition assembly was not. I have an extra switch if you need it. What problem are you solving? Sorry could not get the procedure to upload. Will try later. If no one else posts it you can PM me your email address and I will email it to you.
 

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1984 300SD, 1994 S350
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46 Posts
Discussion Starter #6
I have a new switch block to replace the old one. I think it is the problem I'm having with the HVAC not working, no power. Every once in a while though, when I turn on the ignition to let the glow plugs warm up, the fan will come on, then when I turn the ignition the rest of the way to start, the fan goes back off. I think the ACC portion is not making contact any more in the on position, so it needs to be changed out. I guess the real question is what the procedure to remove the ignition assembly ?
 

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1981 300 SD, 1994 C280, 1990 560 SEC
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618 Posts
Still can't upload MB procedure for this. Will email tonight if you send me your email. From memory. Remove tumbler (if you haven't done that there is a youtube video out there on a w123), remove instrument cluster, remove steering wheel, remove lower cover below steering wheel, loosen bolts that hold steering wheel column, remove switch plug, push in pin that holds ignition to steering wheel, disconnect vacuum lines to ignition and another electrical connection and then work the thing out. In the end it was easier than I thought it was going to be.

Have you confirmed that you are not getting power to fuse 11 when the key is on? If you have power to fuse 11 (or from it) then it is not your ignition switch.

Good luck!
 

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1984 300SD, 1994 S350
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46 Posts
Discussion Starter #8
Yes, I have no power on Fuse # 11. I have a new electrical block, just can't figure out how get the ignition assembly out to replace it.
 

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Two '87 570SECs, one '87 560SEL
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4,443 Posts
My '82 300D had an intermittent interior fan for the climate control system. It was cracked printed circuit board (PCB) solder joints in the pushbutton switch assembly. There are two large wiring harnesses that plug in on the sides of the switch assembly and one of those had wiggled itself enough that it cracked the solder joint between the PCB and the harness plug.

Took me a year to find that it was the problem, a couple of hours to get that switch assembly apart, and five minutes to fix it with fresh solder.
 

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1987 300SDL
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4 Posts
Here are the instructions, uploaded for me this time. Let me know where you are stuck and I will try to help.
Thanks for uploading this! My Dad had a guy who came in to replace the ignition switch while I was at work, and the guy pulled everything out but didn't put it back and we haven't been able to get him to come and fix it. So I'm not quite sure how it goes back together. I will try and post some pics this weekend if I can get to it.

If there are any other sections in the manual on putting the steering wheel/steering column/ignition switch back together, I would greatly appreciate them too; can't my hands on a manual before this weekend.
 

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1987 300SDL
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4 Posts
Thanks for those files! They helped me figure out a lot of larger details in the process. I got it all back together, but I think I have a problem with the NSS. After putting everything back together it started up just fine in park, after not being started for about four months. I'm guessing the NSS could have reset or something by then? But now it will only start in neutral. Looking at other threads right now
 
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