Who says you can put a non-W123 tach in a W123
 

Well I finally got what I wanted, a tach in my 280CE that is. I bought a diesel tach from a guy on MS and thought it would work, but it didn’t, I couldn’t even adjust it to read correct. So I went to the JY and bought 2 tachs from a 4cyl 190 and a 6cyl 190. So I mounted the 190 tach and its gut to my W123 back plate so it would screw into the cluster. Well it turns out that the W201 faceplate is a little smaller than the W123 housing so it had a gap in the top of it (see pic). So I though I would try to put the W123 diesel face plate on the W201 tach guts and adjust it to read correct. Well that worked, so now it fits properly and read properly. I have a hand held tach so that how I adjusted it correctly. Here are the pics, what do you think?

The 190 tach in the W123 housing, see the gap at the top:

http://i42.photobucket.com/albums/e3...y/DSCN0355.jpg

The final result, the diesel faceplate mounted to the W201 tach guts:

http://i42.photobucket.com/albums/e3...y/DSCN0361.jpg

Congratulations! It looks like your persistence paid off. Just out of curiosity, did you ever consider a tach from a W107?

Yeah but the faceplate was 1/4 inch to big, it probably wouldn't even fit in the cluster.

Except for issue of fit, I would suspect any tach that gets a reading from a negative coil lead and a distributor input would work fine. The diesel tach's circuit is different, which is why it didn't work for your case.

Congrats too for your persistence. I have a ton of completed efforts that I had been initially told "wouldn't work"... ;)