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1984 300SD
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Discussion Starter #1
In reading through some other threads, I found one that said there's a circular thing on the top of the driver's side front wheel well that if you unscrew it and put something between the connectors it will fix the tach problem.

Well.... I found the circular thing and next to it is a plug in that I noticed was disconnected. What is this for? I'm attaching two pics; one is a close up and notice the plug in beneath the circular thing. It was unplugged. Should I plug it in? What does it do?
Thanks for your help!
 

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'80 500SE AMG '80 300SD '78 450SLC '00 Passat GLX Wagon
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Does first gear work? I'm not sure if it's the same as my 1980 SD but on mine the tranny shifts into 2nd when you have stopped and put your foot on the brake, then back into first once you get going. It's part of the overload protection relay and when my tranny had a habit of getting stuck in first i discconected it to cure it. Could be someone has done the same- I didn't realy notice any difference since unless it was floored the car was in 1st for a very short time. I'd go ahead and plug it in and see what happens. Hope this has helped, your car could be very different.
 

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Discussion Starter #3
Thank you. This will sound stupid but.....

I believe 1st gear works because I notice 3 shifts (1st to second; second to third and third to 4th) so I'm assuming that this means first works, right?

However, there isn't a "1" on the shifter - it starts at "2". Not sure what that means?
 

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Shawnna - 4/23/2005 11:41 PM

Thank you. This will sound stupid but.....

I believe 1st gear works because I notice 3 shifts (1st to second; second to third and third to 4th) so I'm assuming that this means first works, right?

However, there isn't a "1" on the shifter - it starts at "2". Not sure what that means?
If you notice 3 shifts it's working right, a good thing since my whole tranny blew shortly after the first gear thing started acting up. It could also just be a short, my SD has a few of them and the tach would often do what you describe if it was raining. As long as it's just the tach jumpng and not the real RPMs it's not that important, it's not like you are going to redline your SD. At least I hope not[:)]
 

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1991 500SEC sub 50K mi. 1987 560SEC Now 150K mi. 2018
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Hi Shawna,

How was your trip home, other than the tachometer?

You are correct regarding the connections. I came across this article a while ago, and although I don't now about deisels, I believe it will apply to your car.

http://electric.articles.*/300tachamp/

Hope this helps. MBL

*I have troubles with links to this page, replace the * with mb z.org (without the space). There you will find an article on the tach amplifier & those poor pin connections.
 

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1991 500SEC sub 50K mi. 1987 560SEC Now 150K mi. 2018
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Hi Shawna,

Your connector is Plug/Jack C164 which connects the Cruise Control Amp to the Cruise Control Actuator, provides GND, etc. Enclosed is the info I could find on it.

All 8 pins accounted for......... [:)]

Cheers, MBL
 

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Discussion Starter #8
Thank YOU, MBL! Can you tell me what a "GND" is? Sorry for all the questions but I am trying to fix the little things wrong and the cruise control is one of those!

It was disconnected when I discovered it so my sense is that someone intentionally did this. I also noticed on my trip home that there was one time when the cruise control seemed to be on and accelerating a bit??? I tapped the brake pedal and it 'shut off' like it's suppose to? Could this be possible?

Other than the cruise control, here are my other little things I want to fix and need your insight on:

1. Dash lighting for the speedometer/tach/fluid levels works but is dim. Probably needs new bulbs, right?
2. There are missing lights for the center console controls that need to be fixed. How do I access the bulbs for this section? Could it be something other than bulbs (some of the buttons light, some don't).
3. The existing power antenna appears to be an after market add on (according to the mechanic who did the tuneup) and needs to be replaced. Did these cars (1983 300SD) come with a power antenna? How can I get my hands on the appropriate replacement part?
4. Vacuum door lock/unlock feature doesn't work. Suggestions for fixing?
5. Paint is oxidized on hood and roof - I don't think a detailer can address oxidization, can they? The pics don't show the oxidation but I have attached them for your reference.

Thanks again!

Shawnna
 

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Hi Shawna,

Sorry, Techno-Babble GND = Ground.

Regarding the: "cruise control seemed to be on and accelerating a bit??? I tapped the brake pedal and it 'shut off' like it's suppose to? Could this be possible?" I'm no expert here, but I see in the schematic that the motor control that affects the throttle linkage is connected via pins 4 & 5 through the plug in question... With the plug disconnected as it is..............
The legend in the schematic states: "For cruise control to be engaged, terminal 8 of the amplifier must sense ground through stoplights. When brake switch is closed, ground is electrically removed."

1) You're Correct, the Instrument Cluster bulbs probably need replacement.

2) Need more time.. Imola G.P. about to air on CBS.. [:p]

3) Antenna: Performance Products will prove a good source for you. Have 'em send you a catalogue. It looks as though your car did have a power antenna when new. You have the Antenna rocker switch?

4) Vacuum locks..Need more time G.P. Formula 1 race iminent!

5) Paint... Sorry gotta go rt now

Do look at m b z.org > Articles Lots of good stuff for you there!

Really gotta go now.

I'll ck back [:D] MBL
 

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Discussion Starter #10
Ok. I unscrewed the tach amp and put a piece of cardboard on the bottom and it worked for about 20 minutes - then nothing.

When I took it apart - the plug in plastic crumbled due to age - see photo.

I'm assuming I can get a replacement plug in piece, right? Or do I have to replace both pieces?

Thanks for your help.
 

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Hi Shawna,

OK, the tach worked, so you know its a pretty good bet that the amp is OK & the problem lies with bad connections. I've never looked at one of these plugs before, but you describe exactly what the fellow who wrote the article found. Those m bz.org articles are a good resource for you, i think.
I'm wondering a couple of things here.

1) Is a replacement plug available? PM Jonathan (jhodg5ck), as he has his fingers very close to the W126 'pulse', I've noticed. He's got a lot of good ideas.

2) If a replacement is NOT available, how about carefully removing some of the plastic plug, very slightly crimping the middle of each of the 3 now exposed connector jacks (better contact), inserting the connectors back onto the Tach amp pins & and gluing/sealing it in place with RTV Silicone?

I admit, it seems a stretch, but faced with a possibility of no part available......... This scenario would be a last ditch effort, OK?

Someone else with more hands on knowledge may chime in with another option or a more elegant solution. I hope so! [8)]

Cheers, MBL

Alonso (Renault) held off M. Schumacher (Ferrari) to win the 2005 San Marino Grand Prix. The last 10 laps were REALLY something!
 

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MBL87560SEC - 4/24/2005 3:42 PM

Hi Shawna,

OK, the tach worked, so you know its a pretty good bet that the amp is OK & the problem lies with bad connections. I've never looked at one of these plugs before, but you describe exactly what the fellow who wrote the article found. Those m bz.org articles are a good resource for you, i think.
I'm wondering a couple of things here.

1) Is a replacement plug available? PM Jonathan (jhodg5ck), as he has his fingers very close to the W126 'pulse', I've noticed. He's got a lot of good ideas.

2) If a replacement is NOT available, how about carefully removing some of the plastic plug, very slightly crimping the middle of each of the 3 now exposed connector jacks (better contact), inserting the connectors back onto the Tach amp pins & and gluing/sealing it in place with RTV Silicone?

I admit, it seems a stretch, but faced with a possibility of no part available......... This scenario would be a last ditch effort, OK?

Someone else with more hands on knowledge may chime in with another option or a more elegant solution. I hope so! [8)]

Cheers, MBL

Alonso (Renault) held off M. Schumacher (Ferrari) to win the 2005 San Marino Grand Prix. The last 10 laps were REALLY something!
No kidding. If that didn't improve the chances of F1 becoming more popular in the states nothing will.

BTW Shawna you have a beautiful car, congratulations.
 

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1982 300SD
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Hey, saw you recently bought a 300sd - congratulations! I bought mine about a year ago today and experienced many of the
slight technical issues you've encountered.

Anyway here's a link that got me started -
I asked and they replied, this forum kicks ass,
this specifically refers to the instrument panel illumination, if it not the just your bulbs and I believe tach issues as well.

http://www.mbnz.org/forums/forums/thread-view.asp?tid=1172700&posts=4&hl=
 
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