[C38] Tachometer not working

[jonbix at cox.net]

I own OSPREY, 1983 Cat 38, hailing from Tiverton, RI.  I still have the original Universal diesel which continues to run flawlessly. However my tach is no longer working.  It has been operating intermittently for a few years, then this year it finally died.  My guess is the original tach was simply at the end of it's life.  I replaced the tach myself and it is still not working.  Does anyone have any ideas on what is going on?   By the way, I replaced the alternator about 4 years ago and the tach was working fine after the installation of the new alternator.  I was not sure if replacing the alternator may have had something to do with the tach eventually failing.  Does anyone have any ideas on what is going on or how i may be able to fix this?

Thanks in advance for your help.

Jonathan Bixby
Portsmouth, RI