It was working fine before I did an intake manifold swap. Yes, the tach wire is plugged into the distributor cap.
The needle stays at zero. I always used to point at about 1500 RPM with ignition Off, and then point to zero with ignition On, but now it's at zero either way.
I'd really like to know what changed after swapping the intake and re-installing the distributor...

 

Hello my Friend,

Just curious if you found the cause of this?

 

Not yet. will probably mess with it some more this weekend. I have another tach but have never verified if it works. I just hate to go to the trouble of swapping it out if that's not the problem. Was working fine before sitting over the winter. Finally got around to stabbing the dizzy back in and firing it up 2 weeks ago and tach stayed at zero...

 

*UPDATE*
'Turns out that the tach filter on the firewall is bad. The tach works when bypassing the filter. That's good because even though I have another tach, I really don't feel like swapping it out.
So now the question is; since the tach works without the filter, do I really need a filter??...

 

Without the filter, there's a possibility of noise in the radio, and on other wires in the car. Otherwise, it's not a problem.