Hi this switch is behind my instrument cluster on the top left of my 1984 300D. The yellow tag says instrument. Can anyone tell me what it is? Thanks

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Do you know if your Car has an alarm system?

If it is an alarm system from Mercedes or the Dealer it will have a Trunk opening pull cable somewhere at the bottom drivers side read seat.

On Gassers people used to install anti theft switches that kept the Ignition from working. The only place on a diesel that would work is like the neutral safety switch to keep it from cranking.

A question would be can you reach under and press the switch on and off easily?

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84 300D, 82 Volvo 244Gl Diesel

I looked at the Electrical Diagram for the alarm and there is a "Instrument Cluster Switch" (Closed with instrument cluster pulled out)

However I don't think the Wire Colors in the diagram match.
There is 3 wires on the diagram one brown, BU/YL and BU/YL.
While the number of wires in your pic match and the brown wire matches the other 2 wires don't match the color coding.

In the attached diagram part 537 looks like the same switch and has 3 wire terminals on it.

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84 300D, 82 Volvo 244Gl Diesel

Yes. It is for the factory-installed anti-theft system.

I think the car had an alarm because there is a plug that is disconnected which is located to the left of the drivers side near the trunk lever. After researching that I assume this is part of an alarm?? Anyway, I don't know if this helps but the push switch springs back if not depressed so I assume if the instrument cluster is in, it is always depressed?

That is correct.

So if the big plug down to the left near the trunk lever is unplugged then this push switch is dead and not doing anything? The reason I ask is I am having some center console lighting issues and I want to make sure this button/switch doesn't have anything to do with it. Thanks

I am assuming that:
1. In referring to "the trunk lever", you actually mean the hood release lever.
2. In referring to "the big plug down to the left near the trunk lever", you mean the 13-pin female connector that connects to the alarm relay.
If both assumptions are correct, then yes, based on my experience, this would have nothing to do with central console lighting.

Ha! Yes you are absolutely correct with your assumptions. I will brush up on my terminology. Sorry about that. Thanks

No problem, no need to apologize, happy to help.

Thanks for the follow up. I was not entirely sure as I have never actually seen any of the anti-theft stuff.

I wonder why the color coding of the Wires in the Mercedes Service Manual does not match the actual wiring.

More importantly it is nice to have the pull cable to open you trunk if your vacuum dies and so on.

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84 300D, 82 Volvo 244Gl Diesel

For better or worse and certainly not by choice, I think that I now possess about as much knowledge about the 300CD/D/TD anti-theft system as the people who installed it. Gaining that knowledge was akin to an extended visit to a briar patch.

1. I don't know.
2. Given what I do know about the anti-theft system and it being optional, I would speculate that there is some likelihood that either shortcuts were taken (e.g., "Don't worry about the wire coloring") or that the specifications/manual writing/installation were not completely coordinated and hence the variance.

Great! you can help me sort mine when the times comes