Join Date: Mar 2001
Location: Suisun City, CA
Since you do NOT have a gauge pod with a printed circuit, you do not have the problem of an underdash wiring harness with a pinned connector which precludes a factory tach (like in a 69 and 70). As long as you can mount the tach in the gauge panel and wire the illumination, I would think you can run a wire from the coil secondary + (?) post through the firewall and to the tach, bypassing the underdash wiring harness. The size of the engine does not matter as the tach runs off the coil - 4 firing pulses to a revolution (2 rotations of the crank for every one rotation of the cam, since it is a 4 stroke motor).
Who knows, maybe a guru here would be able to tell us that the underdash harness is the same for tach and non tach and just fish a violet wire out of the loom and plug it in.
Rebuilding a classic mustang is a reality check on your individual state of perfection.