Try connecting an ohmeter between the red and black wire. If it shows continuity it might still be good.
If you could find a tach for a Mustang low-profile Rally-pac the inner tach assembly should be the same and be interchangeable. They look the same to me from what I've seen. I specified 'low-profile' as the earlier 'Hi-profile' was totally different in the face though would probably fit the housing ok. I have actually seen the tach by itself on epay but they don't show up often.
Ron
My low-profile rally-pac, 6 k v8 version, with custom white faces. Normally they are black face with white markings.
