Hi,
I recently acquired an 85 w123 300D. The tachometer does not work, and so I desire to get it going again.
I understand that the tachometer does not use the typical signal path with amplifier, etc., and rather comes from the flywheel via an EGR computer. I would very much like to know how I can trubleshoot the system to determine where my issues are.
As far as I can tell, I need to do the following, with questions intersperced:
-Verify that I have the flywheel pickup. Where do I find this, and where do either end go?
-Verify that the flywheel pickup works. How can I verify this functionality?
-Verify that I have the correct transmission that allows the pickup of signal from the flywheel. What transmission would an 85 w123 have, and how would I tell what I have (in case parts were swapped in the past)?
-Verify functionality of EGR computer that transfers the tach signal. Any ideas how to do this?
-Verify connectivity of tach signal to tachometer in cluster. I should be able to see this by pullng the cluster out, right? If so, it ought to be a 3 pin tach connector, correct?
-Verify overvoltage relay operation. I believe that this relay is what makes the EGR computer work at all, correct? If so, where do I find it, and how do I test it?
-Verfy Klima Relay for A/C operation. Where do I find this relay and how do I test it?
Given that the system in the 85 w123 is different, does this mean that there are changes to the ACC unit in the 85 as well? Mine doesnt seem to work, but I worry about buying parts that might not fit properly, as most places generically lump engines, ACC uinits, etc. from 82-85 all together, though there are apparently differences.
Any insight and assistance would be most appreciated.
Thanks!
JMH