I think I agree with Thomas. My 68 has the electronic tach. It did not work when I bought the car. I sent it out and had it fixed. A few years later my ignition switch fried and took out some of the wiring going thru the tach and it quit. I sent it out again for a less expensive repair. My hunch is the one that runs off the tach generator might be less prone to problems. My 2 cents
David Barnes
68 E-Type FHC