Ever since I bought my 260z my tach has decided it has never wanted to work.  Being that my car is an auto, it hasn't been too much trouble until now.  However, a recent decision to attempt a manual swap and my general annoyance growing, I have decided to fix it.  The issue initially seemed to be a connection issue, as the tachometer would occasionally come back to life mid drive and decide to work perfectly for me, apparently at random times.  I took the dash off, cleaned all the tachometer connections, and reassembled everything.  While the tach was out I tried my best to bench test it, with various methods, and couldn't seem to find a way that worked.  The tach still works occasionally, but not too often.  Before I continue ripping things out and go as far as to replace the tach, does anyone have any wisdom or prior experience to share with me.  Thanks

While the tach is out, you could use a meter like this one to test the signal going to the tach.

https://www.amazon.com/gp/product/B0002LZU7K or https://www.amazon.com/Mrcartool-Digital-Multimeter-500-10000-Temperature/dp/B07VKLKDZL

Connect the positive lead to the blue wire and connect the negative to ground. Put the meter on 6 cyl and start the car. If the signal isn't consistent, then you have a different issue to track down. If the signal is good, your tach is going bad.