Yes, thanks. Great explanation. Got it. I saw a bundle of wires from the 8 pin plug and they were wrapped with the original factory black tape (I assume) and headed toward the engine compartment. I had thought that a problem with the tach's ground might make it work sporadically and not work most of the time. But I do not see now how that is possible unless the other end of the tach wire (going to the front of the engine) could be found and checked. It is so secure at the instrument cluster that even after 35 years I do not think it could come loose. This is a long shot but do you have any idea how I would find the other end of the tach wire/ground wire?

The instrument cluster was a piece of cake except that I dropped all the gears and had to figure out for myself what went where. Did not take clear enough pictures. Hint to the wise. I tightened down the clear plastic cover (the one with the cutout so you can roll the gears) too much and the new gears would not turn. Took me four times of untightening and drive testing to get it right but the gears work fine now. I will say that $75 is way, way too much for Odometer Gears to charge. Way too much. That said I am set for another 35 years now.

Thanks for your help.