Another tach/ac question
 

Hello all,
As some of you might know now I bought my grandmother's 84 300sd this past sunday. Its in good shape and I plan to keep it that way a fix a couple of issues.
The tach is not working and I have been reading up on the amps and pretty much came up with the conclusion that this model does not have the amp on the driver fender wall. I read it is in the passenger footwell. If this is the case is it still an easy fix like the cigarette butt fix or do I need new parts? I also read about the amp getting the signal from the EGR which also affects the air conditioning. Is this the case on the 84? I tried to add a can of R12 to the car but it wouldnt take it even though it did kick on the compressor. It tried to cool and it got a little cool but not really. How can I know if my EGR is disabled?
I just need a little guidance to get me started. I am not knowledgable in the diesel world as I only had this one and another 82 300sd for only a short period of time and the rest of my MB know how is in the gasser realm. Thanks for the input

You should get the service manual on CDs (2) for the wiring diagrams and parts location. They are available from MB and ebay for about $20.

Well this one turned out to be an easy fix. The tach was disconnected behind the instrument cluster. Plugged it back in and it roared back to life. I'm happy.