I haven't seen "Sam" since he posted the original question. Have you?

The Hood Tach is pretty simple caveman stuff. Really. Even one such as I figured out its simple wiring after a few years of ignorance.

It either works correctly or it does not work. Theres no intermittent area for this particular part. There are subtle differences between wiring of original ignition versus HEI, but even that is a caveman thought process. Yes, lets all use the Caveman thing, since some TV station is making a show of it this Fall.